Business Combinations [Abstract] Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Domain] Property, Plant and Equipment, Type [Domain] Customer Premise Equipment [Member] Customer Premise Equipment [Member] Customer premise equipment [Member] Business Acquisition [Axis] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Sky Limited [Member] Sky Limited [Member] Sky Limited [Member] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Customer Relationships [Member] Customer Relationships [Member] Developed Technology and Software [Member] Developed Technology and Software [Member] Developed Technology and Software [Member] Indefinite-lived Intangible Assets [Axis] Indefinite-lived Intangible Assets [Axis] Indefinite-lived Intangible Assets, Major Class Name [Domain] Indefinite-lived Intangible Assets, Major Class Name [Domain] Trade Names [Member] Trade Names [Member] Statistical Measurement [Axis] Statistical Measurement [Axis] Statistical Measurement [Domain] Statistical Measurement [Domain] Minimum [Member] Minimum [Member] Maximum [Member] Maximum [Member] Business Acquisition [Line Items] Business Acquisition [Line Items] Shares acquired, share price (in gbp per share) Business Acquisition, Share Price Percentage of voting interests acquired in period Business Acquisition, Percentage Of Voting Interests Acquired In Period Business Acquisition, Percentage Of Voting Interests Acquired Cash consideration Business Combination, Consideration Transferred Deferred tax assets related to net operating losses Operating Loss Carryforwards, Valuation Allowance Goodwill purchase accounting adjustment Goodwill, Purchase Accounting Adjustments Incremental depreciation and amortization Business Combination, Measurement Period Adjustment, Depreciation And Amortization Business combination measurement period adjustment for depreciation and amortization which was recorded in the current period and related to prior period Property and equipment Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment Estimated useful lives Property, Plant and Equipment, Useful Life Finite-lived intangible assets acquired Finite-lived Intangible Assets Acquired Estimated weighted average useful life Finite-Lived Intangible Asset, Useful Life Indefinite-lived intangible assets acquired Indefinite-lived Intangible Assets Acquired Commitments and Contingencies Disclosure [Abstract] Commitment And Contingencies [Table] Commitment And Contingencies [Table] Commitment And Contingencies [Table] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] NBCUniversal Media LLC [Member] NBCUniversal Media LLC [Member] NBCUniversal Media LLC [Member] Commitment And Contingencies [Line Items] Commitment And Contingencies [Line Items] [Line Items] for Commitment And Contingencies [Table] Schedule of minimum annual programming and talent commitments Contractual Obligation, Fiscal Year Maturity [Table Text Block] Summary of operating lease assets and liabilities Schedule Of Current And Noncurrent Assets And Liabilities [Table Text Block] Schedule Of Current And Noncurrent Assets And Liabilities [Table Text Block] Summary of future minimum rental commitments for operating leases under the new guidance Lessee, Operating Lease, Liability, Maturity [Table Text Block] Summary of future minimum rental commitments for operating leases under the guidance in effect at that time Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block] Schedule of rental expenses charged to operations Rental Expense [Table Text Block] Tabular disclosure of rental expense from operating leases for each period for which an income statement is presented. Goodwill and Intangible Assets Disclosure [Abstract] Schedule of Goodwill [Table] Schedule of Goodwill [Table] Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Operating Segments [Member] Operating Segments [Member] Corporate, Non-Segment [Member] Corporate, Non-Segment [Member] Segments [Axis] Segments [Axis] Segments [Domain] Segments [Domain] Cable Communications [Member] Cable Communications [Member] Cable Communications Member Cable Networks [Member] Cable Networks [Member] Cable Networks Member Broadcast Television [Member] Broadcast Television [Member] Broadcast Television Member Filmed Entertainment [Member] Filmed Entertainment [Member] Filmed Entertainment Member Theme Parks [Member] Theme Parks [Member] Theme Parks Member Goodwill [Line Items] Goodwill [Line Items] Goodwill [Roll Forward] Goodwill [Roll Forward] Balance, beginning of period Goodwill Goodwill Goodwill, Acquired During Period Dispositions Goodwill, Written off Related to Sale of Business Unit Adjustments Goodwill, Other Increase (Decrease) Foreign currency translation Goodwill, Foreign Currency Translation Gain (Loss) Balance, end of period Supplemental Financial Information [Abstract] Statement Of Cash Flows Supplemental Information Abstract Supplemental Financial Information [Table] Supplemental Financial Information [Table] Supplemental Financial Information [Table] Supplemental Financial Information [Line Items] Supplemental Financial Information [Line Items] [Line Items] for Supplemental Financial Information [Table] Supplemental Financial Information Additional Financial Information Disclosure [Text Block] Accounting Policies [Abstract] Recent Accounting Pronouncements [Table] Recent Accounting Pronouncements [Table] Recent Accounting Pronouncements [Table] Recent Accounting Pronouncements [Line Items] Recent Accounting Pronouncements [Line Items] [Line Items] for Recent Accounting Pronouncements [Table] Basis of Presentation Consolidation, Policy [Policy Text Block] Foreign Currency Translation Foreign Currency Transactions and Translations Policy [Policy Text Block] Use of Estimates Use of Estimates, Policy [Policy Text Block] Advertising Cost Advertising Cost [Policy Text Block] Derivative Financial Instruments Derivatives, Policy [Policy Text Block] Fair Value Measurements Fair Value Measurement, Policy [Policy Text Block] Revenue Recognition Revenue from Contract with Customer [Policy Text Block] Film and Television Costs Film And Television Costs [Policy Text Block] Describes an entity's accounting policy for film and television costs. This accounting policy also may address how an entity assesses and measures impairment of film and television costs. Income Taxes Income Tax, Policy [Policy Text Block] Earnings Per Share Earnings Per Share, Policy [Policy Text Block] Recent Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Investments Investment, Policy [Policy Text Block] Impairment Testing of Investments Investments Impairment [Policy Text Block] Disclosure of accounting policy for recognizing and measuring the impairment of long-lived assets. Property and Equipment Property, Plant and Equipment, Policy [Policy Text Block] Goodwill Goodwill and Intangible Assets, Goodwill, Policy [Policy Text Block] Indefinite-Lived Intangible Assets Goodwill and Intangible Assets, Intangible Assets, Indefinite-Lived, Policy [Policy Text Block] Finite-Lived Intangible Assets Goodwill and Intangible Assets, Intangible Assets, Policy [Policy Text Block] Postretirement and Pension Benefits Pension and Other Postretirement Plans, Policy [Policy Text Block] Share-Based Compensation Compensation Related Costs, Policy [Policy Text Block] Leases Lessee, Leases [Policy Text Block] Related Party Transactions [Abstract] Schedule of Related Party Transactions, by Related Party [Table] Schedule of Related Party Transactions, by Related Party [Table] Related Party [Axis] Related Party [Axis] Related Party [Domain] Related Party [Domain] Comcast and Consolidated Subsidiaries [Member] Comcast And Consolidated Subsidiaries [Member] Related Party Transaction [Line Items] Related Party Transaction [Line Items] Revenue Revenues Total costs and expenses Costs and Expenses Interest expense and investment and other income (loss), net Other Income (Expense) Related Party Represents the intercompany transactions with ultimate parent, which are included in interest expense and investment and other income (loss), net. Equity [Abstract] Class of Treasury Stock [Table] Class of Treasury Stock [Table] Share Repurchase Program [Axis] Share Repurchase Program [Axis] Share Repurchase Program [Domain] Share Repurchase Program [Domain] New Authorization [Member] New Authorization [Member] Equity, Class of Treasury Stock [Line Items] Equity, Class of Treasury Stock [Line Items] Cash consideration Payments for Repurchase of Common Stock Shares repurchased (in shares) Stock Repurchased and Retired During Period, Shares Statement of Financial Position [Abstract] Statement [Table] Statement [Table] Class of Stock [Axis] Class of Stock [Axis] Class of Stock [Domain] Class of Stock [Domain] Class A Common Stock [Member] Common Class A [Member] Class B Common Stock [Member] Common Class B [Member] Statement [Line Items] Statement [Line Items] Preferred stock, shares authorized (in shares) Preferred Stock, Shares Authorized Preferred stock, shares issued (in shares) Preferred Stock, Shares Issued Common stock, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Common stock, shares authorized (in shares) Common Stock, Shares Authorized Common stock, shares issued (in shares) Common Stock, Shares, Issued Common stock, shares outstanding (in shares) Common Stock, Shares, Outstanding Treasury stock (in shares) Treasury Stock, Shares Revenue from Contract with Customer [Abstract] Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Revenue [Line Items] Disaggregation of Revenue [Line Items] Disaggregation of revenue Disaggregation of Revenue [Table Text Block] Schedule of receivables, net Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] Other balance sheet accounts Schedule Of Other Balance Sheet Accounts [Table Text Block] Schedule Of Other Balance Sheet Accounts [Table Text Block] Statement of Stockholders' Equity [Abstract] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Redeemable Noncontrolling Interests And Redeemable Subsidiary Preferred Stock [Member] Redeemable Noncontrolling Interests And Redeemable Subsidiary Preferred Stock [Member] Redeemable Noncontrolling Interests and Redeemable Subsidiary Preferred Stock [Member] Common Stock [Member] Common Stock [Member] Member's Capital [Member] Member's Capital [Member] Additional Paid-in Capital [Member] Additional Paid-in Capital [Member] Retained Earnings [Member] Retained Earnings [Member] Treasury Stock at Cost [Member] Treasury Stock [Member] Accumulated Other Comprehensive Income (Loss) [Member] AOCI Attributable to Parent [Member] Noncontrolling Interests [Member] Noncontrolling Interest [Member] Redeemable Noncontrolling Interest [Member] Redeemable Noncontrolling Interest [Member] Increase (Decrease) in Temporary Equity [Roll Forward] Increase (Decrease) in Temporary Equity [Roll Forward] Beginning balance Redeemable Noncontrolling Interest, Equity, Carrying Amount Contributions from (distributions to) noncontrolling interests, net Contributions From And Distributions To Noncontrolling Interests Attributable To Temporary Equity Contributions from and (distributions to) noncontrolling interests attributable to temporary equity. Other Temporary Equity, Other Changes Net income (loss) Net Income (Loss) Attributable to Redeemable Noncontrolling Interest Ending balance Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Beginning balance Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Beginning balance Limited Liability Company (LLC) Members' Equity, Including Portion Attributable to Noncontrolling Interest Cumulative effects of adoption of accounting standards Cumulative Effect of New Accounting Principle in Period of Adoption Stock compensation plans APIC, Share-based Payment Arrangement, Increase for Cost Recognition Repurchases of common stock under repurchase program and employee plans Stock Repurchased and Retired During Period, Value Employee stock purchase plans Stock Issued During Period, Value, Employee Stock Purchase Plan Dividends declared Dividends, Common Stock, Cash Distributions to member Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Declared Other comprehensive income (loss) Other Comprehensive Income (Loss), Net of Tax Contributions from (distributions to) noncontrolling interests, net Contributions From And Distributions To Noncontrolling Interests Contributions from and distributions to noncontrolling interests Contributions from member Member Contribution Contribution from member including, but not limited to, a business, investment or asset. Purchase of Universal Studios Japan noncontrolling interests Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests Other Stockholders' Equity, Other Net Income Attributable to Comcast Corporation Net Income (Loss) Attributable to Parent Net income (loss) Net Income (Loss) Attributable to Noncontrolling Interest Ending balance Ending balance Cash dividends declared per common share (in dollars per share) Common Stock, Dividends, Per Share, Declared Quarterly Financial Information Disclosure [Abstract] Schedule of quarterly financial information Quarterly Financial Information [Table Text Block] SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract] SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Table] SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Table] SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items] SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items] Schedule II - Valuation and Qualifying Accounts SEC Schedule, 12-09, Schedule of Valuation and Qualifying Accounts Disclosure [Text Block] Operating income Operating Income (Loss) Net income attributable to Comcast Corporation Basic earnings per common share attributable to Comcast Corporation shareholders (in dollars per share) Earnings Per Share, Basic Diluted earnings per common share attributable to Comcast Corporation shareholders (in dollars per share) Earnings Per Share, Diluted Dividends declared per common share (in dollars per share) Earnings Per Share [Abstract] Computation of diluted EPS Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Debt Disclosure [Abstract] Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Debt Instrument [Line Items] Debt Instrument [Line Items] Schedule of Long-Term Debt Schedule of Debt [Table Text Block] Debt Maturities Schedule of Maturities of Long-term Debt [Table Text Block] Income Tax Disclosure [Abstract] Income Taxes [Table] Income Taxes [Table] Income Taxes [Table] Income Tax Authority [Axis] Income Tax Authority [Axis] Income Tax Authority [Domain] Income Tax Authority [Domain] Federal Tax Authority [Member] Domestic Tax Authority [Member] Foreign Tax Authority [Member] Foreign Tax Authority [Member] Income Taxes [Line Items] Income Taxes [Line Items] [Line Items] for Income Taxes [Table] Federal corporate income tax rate Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent Reduction of net deferred tax liabilities Effective Income Tax Rate Reconciliation tax reform legislation Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to tax reform legislation. Deferred tax liability attributable to temporary differences in other comprehensive income Changes In Net Deferred Tax Liability Related To Other Comprehensive Income Changes in net deferred tax liability that were not recorded as deferred income tax benefit (expense) associated with items included in other comprehensive income (loss) Change in net deferred tax liability related to acquisitions Change In Net Deferred Tax Liability Related To Acquisitions Changes in net deferred tax liability that were not recorded as deferred income tax benefit (expense) related to acquisitions. Net deferred tax liability, franchise rights Deferred Tax Liability Franchise Rights Amount of net deferred tax liabilities related to cable franchise rights that will remain unchanged unless an impairment is recognized or a cable franchise is disposed. Operating loss carryforwards Operating Loss Carryforwards Liability for uncertain tax positions Liability for Uncertainty in Income Taxes, Noncurrent Unrecognized tax benefits that would impact effective tax rate Unrecognized Tax Benefits that Would Impact Effective Tax Rate Unrecognized tax benefits, interest on income taxes accrued Unrecognized Tax Benefits, Interest on Income Taxes Accrued Schedule of cash payments for interest and income taxes Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Schedule of cash, cash equivalents and restricted cash ScheduleOfCashCashEquivalentsAndRestrictedCash [Table Text Block] Tabular disclosure of the components of cash, cash equivalents and restricted cash. Schedule of accumulated other comprehensive income (loss) Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] Unrealized gains (losses) on marketable securities AOCI, Debt Securities, Available-for-sale, Adjustment, after Tax Deferred gains (losses) on cash flow hedges AOCI, Cash Flow Hedge, Cumulative Gain (Loss), after Tax Unrecognized gains (losses) on employee benefit obligations Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax Cumulative translation adjustments Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax Accumulated other comprehensive income (loss), net of deferred taxes Accumulated Other Comprehensive Income (Loss), Net of Tax Assets Assets [Abstract] Current Assets: Assets, Current [Abstract] Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Receivables, net Accounts Receivable, after Allowance for Credit Loss, Current Programming rights Programming Rights, Current The current portion of acquired television and cable networks programming rights recorded on the balance sheet. Includes multi-year programming arrangements, acquired movies, series and other programs. Carrying amount is stated at the lower of cost, less accumulated amortization, or net realizable value at the balance sheet date. Notes receivable from Comcast Notes Receivable From Ultimate Parent, Current Total current amount due from Parent including cash management arrangement under the matching revolving credit facilities as of the balance sheet date. Other current assets Other Assets, Current Total current assets Assets, Current Film and television costs Film And Television Costs The carrying amount of owned films, television series and other television productions and noncurrent acquired television and cable networks programming rights recorded on the balance sheet. Owned films, television series and other television production costs include capitalizable production costs, including direct costs, production overhead, print costs, development costs and interest. Film and television rights include multi-year programming arrangements, acquired movies, series and other programs. The carrying amount is stated at the lower of cost, less accumulated amortization, or net realizable/fair value at the balance sheet date. Investments Long-term Investments Investment securing collateralized obligation Investment Securing Collateralized Obligation Carrying amount of investment presented separately as investment securing collateralized obligation that is partially securing an obligation. Note receivable from Comcast Note Receivable From Ultimate Parent, Noncurrent Note Receivable From Ultimate Parent, Noncurrent Property and equipment, net Property, Plant and Equipment, Net Goodwill Franchise rights Indefinite-Lived Franchise Rights Intangible assets, net Intangible Assets, Net (Excluding Goodwill) Other intangible assets, net Other Intangible Assets, Net Other noncurrent assets, net Other Assets, Noncurrent Total assets Assets Liabilities and Equity Liabilities and Equity [Abstract] Current Liabilities: Liabilities, Current [Abstract] Accounts payable and accrued expenses related to trade creditors Accounts Payable, Current Accrued participations and residuals Accrued Participations And Residuals, Current The total amount of participations, residual and royalty expenses due to another party in less than one year. Royalty expenses are due to content creators, including artists, authors and other talent; participations includes amounts to financial participants in films, including actors, directors, and producers, for contractually defined participations in a film's net profit or gross receipts; residuals include amounts due to unions and guilds. Program obligations Program Rights Obligations, Current Deferred revenue Deferred Revenue, Current Accrued expenses and other current liabilities Accrued Liabilities, Current Notes payable to Comcast Note Payable To Ultimate Parent The total amount due to Parent, with respect to cash management arrangements under the matching revolving credit notes, as of the balance sheet date. Current portion of long-term debt Debt, Current Total current liabilities Liabilities, Current Long-term debt, less current portion Long-term Debt and Lease Obligation Collateralized obligation Collateralized Obligation Carrying amount of obligation presented separately as collateralized obligation that is secured by assets. Accrued participations, residuals and program obligations Accrued Participations Residuals And Program Obligations, Noncurrent The noncurrent amount of participations, residual, royalty expenses and program obligations due to another party. Royalty expenses are due to content creators, including artists, authors and other talent; participations includes amounts to financial participants in films, including actors, directors, and producers, for contractually defined participations in a film's net profit or gross receipts; residuals include amounts due to unions and guilds. Deferred income taxes Deferred Income Tax Liabilities, Net Other noncurrent liabilities Other Liabilities, Noncurrent Commitments and contingencies Commitments and Contingencies Redeemable noncontrolling interests Equity: Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Preferred stock—authorized, 20,000,000 shares; issued, zero Preferred Stock, Value, Issued Member’s capital Members' Capital Common stock Common Stock, Value, Issued Additional paid-in capital Additional Paid in Capital Retained earnings Retained Earnings (Accumulated Deficit) Treasury stock, 872,791,028 Class A common shares Treasury Stock, Value Accumulated other comprehensive income (loss) Total NBCUniversal member’s equity Members' Equity Total Comcast Corporation shareholders’ equity Stockholders' Equity Attributable to Parent Noncontrolling interests Members' Equity Attributable to Noncontrolling Interest Noncontrolling interests Stockholders' Equity Attributable to Noncontrolling Interest Total equity Total equity Total liabilities and equity Liabilities and Equity Long-term Debt, Fiscal Year Maturity [Abstract] Long-term Debt, Fiscal Year Maturity [Abstract] 2020 Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months 2021 Long-term Debt, Maturities, Repayments of Principal in Year Two 2022 Long-term Debt, Maturities, Repayments of Principal in Year Three 2023 Long-term Debt, Maturities, Repayments of Principal in Year Four 2024 Long-term Debt, Maturities, Repayments of Principal in Year Five Thereafter Long-term Debt, Maturities, Repayments of Principal after Year Five Segment Reporting [Abstract] Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Customer [Axis] Customer [Axis] Customer [Domain] Customer [Domain] Residential [Member] Residential Customers [Member] Residential Customers [Member] Business Customers [Member] Business Customers [Member] Business Customers [Member] Product and Service [Axis] Product and Service [Axis] Product and Service [Domain] Product and Service [Domain] High-speed Internet Customers [Member] High-speed Internet Customers [Member] High-speed Internet Customers [Member] Video Customers [Member] Video Customers [Member] Video Customers [Member] Voice Customers [Member] Voice Customers [Member] Voice Customers [Member] Security and Automation Customers [Member] Security And Automation Customers [Member] Security And Automation Customers [Member] Wireless Phone Service [Member] Wireless Lines [Member] Wireless Lines [Member] Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Total customer relationships Total Customer Relationships Represents the number of residential and business customers that subscribe to at least one of our four primary services of video, high-speed Internet, voice, and security and automation. Number of customers Number Of Customers Represents the number of customers that subscribe to our services. Number of activated lines Number Of Activated Lines Number Of Activated Lines Retail customer relationships Total Retail Customer Relationships Represents the number of retail customers that subscribe to at least one of the primary services of video, high-speed internet, voice, and wireless phone services. Condensed Financial Information Disclosure [Abstract] Condensed Consolidating Statement of Income Condensed Income Statement [Table Text Block] Condensed Consolidating Statement of Cash Flows Condensed Cash Flow Statement [Table Text Block] Condensed Consolidating Balance Sheet Condensed Balance Sheet [Table Text Block] Goodwill And Intangible Assets [Table] Goodwill And Intangible Assets [Table] Goodwill And Intangible Assets [Table] Goodwill And Intangible Assets [Line Items] Goodwill And Intangible Assets [Line Items] [Line Items] for Goodwill And Intangible Assets [Table] Schedule of Goodwill Schedule of Goodwill [Table Text Block] Other Intangible Assets Intangible Assets Disclosure [Text Block] Amortization of Intangible Assets Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block] Condensed Cash Flow Statement [Table] Condensed Cash Flow Statement [Table] Comcast Holdings [Member] Comcast Holdings [Member] Comcast Holdings CCCL Parent [Member] CCCL Parent [Member] CCCL Parent NBCUniversal Media Parent [Member] NBCUniversal Media Parent [Member] Consolidated Entities [Axis] Consolidated Entities [Axis] Consolidated Entities [Domain] Consolidated Entities [Domain] Comcast Parent [Member] Parent Company [Member] Subsidiary Issuer [Member] Subsidiary Issuer [Member] Guarantor Subsidiaries [Member] Guarantor Subsidiaries [Member] Non-Guarantor Subsidiaries [Member] Non-Guarantor Subsidiaries [Member] Reportable Legal Entities [Member] Reportable Legal Entities [Member] Elimination and Consolidation Adjustments [Member] Consolidation, Eliminations [Member] Condensed Cash Flow Statements, Captions [Line Items] Condensed Cash Flow Statements, Captions [Line Items] Operating Activities Net Cash Provided by (Used in) Operating Activities [Abstract] Net cash provided by (used in) operating activities Net Cash Provided by (Used in) Operating Activities Investing Activities Net Cash Provided by (Used in) Investing Activities [Abstract] Net transactions with affiliates Net transactions with affiliates Net transactions with affiliates. Capital expenditures Payments to Acquire Property, Plant, and Equipment Cash paid for intangible assets Payments to Acquire Intangible Assets Acquisitions and construction of real estate properties Payments For Acquisitions And Construction Of Real Estate Properties The cash outflow for the acquisition and construction of buildings (properties) whether for investment or use. Construction of Universal Beijing Resort Payments For Construction Of Theme Park The cash outflow associated with the construction of a theme park. Acquisitions, net of cash acquired Payments to Acquire Businesses, Net of Cash Acquired Proceeds from sales of businesses and investments Proceeds From Sales Of Businesses And Investments The cash inflow associated with the sale of businesses and investments, if any, during the period. Purchases of investments Payments to Acquire Investments Other Payments for (Proceeds from) Other Investing Activities Net cash provided by (used in) investing activities Net Cash Provided by (Used in) Investing Activities Financing Activities Net Cash Provided by (Used in) Financing Activities [Abstract] Proceeds from (repayments of) short-term borrowings, net Proceeds from (Repayments of) Short-term Debt Proceeds from borrowings Proceeds from Issuance of Long-term Debt Proceeds from collateralized obligation Proceeds From Collateralized Obligation The cash inflow from amounts received from the issuance of an obligation that is secured by assets and is presented separately as proceeds from collateralized obligation. Repurchases and repayments of debt Repayments of Other Debt Repurchases of common stock under repurchase program and employee plans Dividends paid Payments of Dividends Purchase of Universal Studios Japan noncontrolling interests Payments to Noncontrolling Interests Distributions to noncontrolling interests and dividends for redeemable subsidiary preferred stock Distributions To Noncontrolling Interests And Dividends For Redeemable Subsidiary Preferred Stock The cash outflow related to distributions to noncontrolling interests and dividends for redeemable subsidiary preferred stock. Other Proceeds from (Payments for) Other Financing Activities Net cash provided by (used in) financing activities Net Cash Provided by (Used in) Financing Activities Impact of foreign currency on cash, cash equivalents and restricted cash Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Increase (decrease) in cash and cash equivalents and restricted cash Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Cash, cash equivalents and restricted cash, beginning of year Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Cash, cash equivalents and restricted cash, end of year Statement of Comprehensive Income [Abstract] Unrealized gains (losses) on marketable securities, deferred taxes Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax Deferred gains (losses) on cash flow hedges, deferred taxes Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification, Tax Realized (gains) losses on marketable securities, deferred taxes Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax Realized (gains) losses on cash flow hedges, deferred taxes Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, Tax Employee benefit obligations, deferred taxes Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax Currency translation adjustments, deferred tax Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax Eliminations [Member] Segment Reconciling Items [Member] NBCUniversal Segments [Member] NBCUniversal Segments [Member] Financial Data by Business Segment Segment Reporting Information, Profit (Loss) [Abstract] Adjusted EBITDA Adjusted EBITDA The measure used to evaluate the profitability of operating segments. Depreciation and Amortization Depreciation, Depletion and Amortization, Nonproduction Capital Expenditures Cash Paid for Intangible Assets Residential [Member] Residential [Member] Residential [Member] Business Services [Member] Business Services [Member] Business Services [Member] Distribution [Member] Distribution [Member] Distribution Advertising [Member] Advertising [Member] Theatrical [Member] Theatrical [Member] Theatrical [Member] Content Licensing [Member] Content Licensing [Member] Content Licensing [Member] Home Entertainment [Member] Home Entertainment [Member] Home Entertainment [Member] Direct To Consumer [Member] Direct To Consumer [Member] Direct To Consumer [Member] Revenue [Line Items] Term of contract Revenue, Performance Obligation, Description Of Timing, Term Of Contract Revenue, Performance Obligation, Description Of Timing, Term Of Contract Annual revenue that estimates remaining performance obligations Annual Revenue That Estimates Remaining Performance Obligations Years of annual revenue that estimate revenue for performance obligations that have not been recognized as revenue Timing period of recognition Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period Expected payment terms Revenue, Performance Obligation, Description Of Payment Terms, Period Revenue, Performance Obligation, Description Of Payment Terms, Period Share-based Payment Arrangement [Abstract] Share-Based Compensation Share-based Payment Arrangement [Text Block] Tax Adjustments [Axis] Tax Adjustments [Axis] Tax Adjustments [Axis] Tax Adjustments [Domain] Tax Adjustments [Domain] Tax Adjustments [Domain] Adjustments to uncertain and effectively settled tax positions, net [Member] Uncertain And Effectively Settled Tax Positions, Net [Member] Uncertain And Effectively Settled Tax Positions, Net Member Accrued interest on uncertain and effectively settled tax positions, net [Member] Accrued Interest and Penalties On Uncertain And Effectively Settled Tax Positions Net [Member] Accrued Interest and Penalties On Uncertain And Effectively Settled Tax Positions Net [Member] Federal tax at statutory rate Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount State income taxes, net of federal benefit Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount Foreign income taxed at different rates Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Amount Nontaxable income attributable to noncontrolling interests Effective Income Tax Rate Reconciliation, Noncontrolling Interest Income (Loss), Amount Other adjustments Effective Income Tax Rate Reconciliation, Other Adjustments, Amount Excess tax benefits recognized on share-based compensation Effective Income Tax Rate Reconciliation, Tax Expense (Benefit), Share-based Payment Arrangement, Amount Tax legislation Income tax (expense) benefit Income Tax Expense (Benefit) Schedule of income before income taxes Schedule of Income before Income Tax, Domestic and Foreign [Table Text Block] Schedule for the components of income tax expense Schedule of Components of Income Tax Expense (Benefit) [Table Text Block] Schedule of items that effect income tax expense Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Schedule of the components of net deferred tax liability Schedule of Deferred Tax Assets and Liabilities [Table Text Block] Reconciliation of unrecognized tax benefits Summary of Income Tax Contingencies [Table Text Block] Deferred Tax Assets: Deferred Tax Assets, Net [Abstract] Net operating loss and other loss carryforwards Deferred Tax Assets, Operating Loss And Other Loss Carryforwards Deferred Tax Assets, Operating Loss And Other Loss Carryforwards Nondeductible accruals and other Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Other Less: Valuation allowance Deferred Tax Assets, Valuation Allowance Total deferred tax assets, net of valuation allowance Deferred Tax Assets, Net of Valuation Allowance Deferred Tax Liabilities: Deferred Tax Liabilities, Net [Abstract] Differences between book and tax basis of property and equipment and intangible assets Deferred Tax Liabilities, Property, Plant And Equipment And Intangible Assets Amount before allocation of valuation allowances of deferred tax liability attributable to deductible temporary differences from property and equipment and intangible assets. Differences between book and tax basis of investments DeferredTaxLiabilityInvestments Amount of deferred tax liability attributable to taxable temporary differences from investments. Differences between book and tax basis of long-term debt Deferred Tax Liabilities, Long-Term Debt Amount before allocation of valuation allowances of deferred tax liability attributable to deductible temporary differences from long-term debt. Differences between book and tax basis of foreign subsidiaries and undistributed foreign earnings Deferred Tax Liabilities, Undistributed Foreign Earnings Total deferred tax liabilities Deferred Tax Liabilities, Gross Net deferred tax liability Deferred Tax Liabilities, Net Investments [Abstract] Schedule of Fair Value Method Investments [Table] Schedule of Fair Value Method Investments [Table] Schedule of Fair Value Method Investments [Table] Investment, Name [Axis] Investment, Name [Axis] Investment, Name [Domain] Investment, Name [Domain] Snap [Member] Snap [Member] Snap [Member] Peloton [Member] Peloton [Member] Peloton Schedule of Marketable Equity Securities [Line Items] Schedule of Fair Value Method Investments [Line Items] [Line Items] for Schedule of Fair Value Method Investments [Table] Payments to acquire marketable equity securities Payments to Acquire Marketable Securities Marketable equity securities, recognized realized gains (losses) Equity Securities, FV-NI, Realized Gain (Loss) Marketable equity securities, recognized unrealized gains (losses) Equity Securities, FV-NI, Unrealized Gain (Loss) Realized and unrealized gains (losses) on equity securities, net Equity Securities, FV-NI, Gain (Loss) Marketable equity securities Equity Securities, FV-NI Nonmarketable equity securities Equity Securities without Readily Determinable Fair Value, Amount Equity [Table] Equity [Table] Equity [Table] Equity [Line Items] Equity [Line Items] [Line Items] for Equity [Table] Common stock, shares outstanding at beginning of period (in shares) Stock compensation plans (in shares) Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture Repurchases and retirements of common stock (in shares) Employee stock purchase plan (in shares) Stock Issued During Period, Shares, Employee Stock Purchase Plans Common stock, shares outstanding at end of period (in shares) Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Award Type [Axis] Award Type [Axis] Award Type [Domain] Award Type [Domain] Restricted share units [Member] Restricted Stock Units (RSUs) [Member] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Stock options granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross Weighted-average exercise price of awards granted during the year (in dollars per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price Stock options outstanding (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Weighted-average exercise price of shares outstanding (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Awards granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Awards nonvested (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Weighted-average fair value at grant date of nonvested awards (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Cash Payments for Interest and Income Taxes Supplemental Cash Flow Information [Abstract] Interest Interest Paid, Excluding Capitalized Interest, Operating Activities Income taxes Income Taxes Paid, Net Universal Studios Japan [Member] Universal Studios Japan [Member] Payments to acquire additional interest in noncontrolling interest Segment Information Segment Reporting Disclosure [Text Block] Income Statement [Abstract] Costs and Expenses: Costs and Expenses [Abstract] Programming and production Programming And Production Costs The amount of expense recognized in the period for costs associated with video programming and content acquisition and production costs. Programming expenses include the fees paid to license the programming distributed to video customers, such as the programming license fees charged by cable networks and fees charged for retransmission of the signals from local broadcast television stations. Production costs include the amortization of owned and acquired programming, sports rights, direct production costs, residual and participation payments, production overhead, costs associated with the distribution of programming to third-party networks and other distribution platforms, and on-air talent costs. It also includes the amortization of capitalized theatrical film production and acquisition costs and distribution expenses. Other operating and administrative Other Operating And Administrative Other operating and administrative expense recognized in the period not presented separately. Advertising, marketing and promotion Marketing and Advertising Expense Depreciation Depreciation Amortization Amortization of Intangible Assets Other operating gains Gain (Loss) on Disposition of Assets Total costs and expenses Operating income (loss) Interest expense Interest Expense Investment and other income (loss), net Nonoperating Income (Expense) Income (loss) before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Income tax (expense) benefit Net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Less: Net income attributable to noncontrolling interests and redeemable subsidiary preferred stock Net Income (Loss) Attributable To Noncontrolling Interests And Redeemable Subsidiary Preferred Stock Amount of net income (loss) attributable to noncontrolling interest and dividends on redeemable subsidiary preferred stock. Less: Net income attributable to noncontrolling interests Net income attributable to Comcast Corporation Goodwill and Intangible Assets Goodwill and Intangible Assets Disclosure [Text Block] Other current assets Notes receivable from Comcast, current Note receivable from Comcast, noncurrent Notes payable to Comcast Notes Payable To Ultimate Parent The total amount due to Ultimate Parent, including cash management arrangement under the matching revolving credit facilities as of the balance sheet date. Long-term debt Revenue Revenue from Contract with Customer [Text Block] New Accounting Pronouncements or Change in Accounting Principle [Table] New Accounting Pronouncements or Change in Accounting Principle [Table] Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] Accounting Standards Update 2016-02 [Member] Accounting Standards Update 2016-02 [Member] New Accounting Pronouncements or Change in Accounting Principle [Line Items] New Accounting Pronouncements or Change in Accounting Principle [Line Items] Operating lease assets Operating Lease, Right-of-Use Asset Operating lease liabilities Operating Lease, Liability Finance lease liabilities Finance Lease, Liability Additional finance lease liability Additional Finance Lease Liability Present value of lessee's discounted obligation for lease payments from finance lease for additional contracts determined to be leases in connection with the business acquisition. Property, Plant and Equipment [Abstract] Property, Plant and Equipment [Table] Property, Plant and Equipment [Table] Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Property and Equipment Property, Plant and Equipment Disclosure [Text Block] Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Organization, Consolidation and Presentation of Financial Statements [Abstract] Business And Basis Of Presentation [Table] Business And Basis Of Presentation [Table] Business And Basis Of Presentation [Table] Business And Basis Of Presentation [Line Items] Business And Basis Of Presentation [Line Items] Business And Basis Of Presentation Number of primary businesses Number Of Businesses Number Of Businesses Number of reportable segments Number of Reportable Segments Current (Expense) Benefit: Current Income Tax Expense (Benefit), Continuing Operations [Abstract] Federal Current Federal Tax Expense (Benefit) State Current State and Local Tax Expense (Benefit) Foreign Current Foreign Tax Expense (Benefit) Current income tax (expense) benefit Current Income Tax Expense (Benefit) Deferred (Expense) Benefit: Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract] Federal Deferred Federal Income Tax Expense (Benefit) State Deferred State and Local Income Tax Expense (Benefit) Foreign Deferred Foreign Income Tax Expense (Benefit) Deferred income tax (expense) benefit Deferred Income Tax Expense (Benefit) Withholding tax expense Foreign Withholding Tax Expense The amount of tax liability incurred by the Company in licensing its content to non-US territories. U.S. domestic tax expense Domestic Tax Expense Benefit Amount of current and deferred income tax expense (benefit) attributable to income (loss) from continuing domestic operations within the country of domicile of the entity. Schedule Of Intangible Assets [Table] Schedule Of Intangible Assets [Table] FCC Spectrum [Member] Licensing Agreements [Member] FCC Spectrum Auction [Line Items] FCC Spectrum Auction [Line Items] FCC Spectrum Auction [Line Items] Proceeds from FCC spectrum auction Proceeds from Sale of Intangible Assets Gain on sale of spectrum rights Gain (Loss) on Disposition of Intangible Assets Amount of spectrum acquired Indefinite-lived Intangible Assets (Excluding Goodwill) Deposit to acquire intangible asset Deposit To Acquire Intangible Asset Deposit paid in a prior period for the right to an intangible asset in a future period. Rental expense Operating Leases, Rent Expense Debt Securities, Trading, and Equity Securities, FV-NI [Table] Debt Securities, Trading, and Equity Securities, FV-NI [Table] Investment and Other Income (Loss), Net [Line Items] Debt and Equity Securities, FV-NI [Line Items] Equity in net income (losses) of investees, net Income (Loss) from Equity Method Investments Other income (loss), net Other Income Loss Net Nonoperating income (losses), net recorded in the income statement that are not separately stated. Investment and other income (loss), net Voting power Common Stock Voting Power Common Stock Voting Power Number of votes entitled of each class B common stock Number Of Votes Entitled Of Each Class B Common Stock Number of votes entitled to vote for each share of Class B common stock share. Stock repurchase program, authorized amount Stock Repurchase Program, Authorized Amount Remaining authorized repurchase amount Stock Repurchase Program, Remaining Authorized Repurchase Amount Earnings Per Share Earnings Per Share [Text Block] Deferred gains (losses) on cash flow hedges Unrecognized gains (losses) on employee benefit obligations Cumulative translation adjustments Investment Holdings [Table] Investment Holdings [Table] Air Touch [Member] Air Touch [Member] Air Touch [member] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Level 2 [Member] Fair Value, Inputs, Level 2 [Member] Schedule of Other Investments [Line Items] Investment Holdings [Line Items] Number of series of preferred stock Number of Preferred Stock Series Number of Preferred Stock Series Held to maturity investment, Current Debt Securities, Held-to-maturity, Current Held to maturity investment, Noncurrent Debt Securities, Held-to-maturity, Noncurrent Fair value of held to maturity investment redeemable preferred shares Debt Securities, Held-to-maturity, Fair Value Preferred stock aggregate redemption value Preferred Stock Aggregate Redemption Value Preferred stock aggregate redemption value at a future date. Preferred stock redemption value Preferred Stock, Redemption Value Preferred stock redemption value at a future date. Redeemable subsidiary preferred shares Carrying Amount Of Redeemable Preferred Stock Carrying amount of redeemable preferred stock Fair value of redeemable preferred shares Fair Value Of Redeemable Preferred Shares Fair value of our redeemable subsidiary preferred shares and/or stock Nonredeemable subsidiary preferred shares Nonredeemable Preferred Stock Nonredeemable preferred stock issued by a wholly owned subsidiary of the company. Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Commercial Paper [Member] Commercial Paper [Member] Revolving Credit Facilities [Member] Revolving Credit Facility [Member] Term Loans [Member] Term Loans [Member] Term Loans [Member] Senior notes with maturities of 5 years or less, at face value [Member] Senior notes with maturities of 5 years or less, at face value [Member] Senior notes with maturities of 5 years or less [Member] Senior notes with maturities between 5 and 10 years, at face value [Member] Senior notes with maturities between 5 and 10 years, at face value [Member] Senior notes with maturities between 5 and 10 years [Member] Senior notes with maturities greater than 10 years, at face value [Member] Senior notes with maturities greater than 10 years, at face value [Member] Senior notes with maturities greater than 10 years [Member] 4.00% Notes Due 2049 To Comcast [Member] 4.00% Notes Due 2049 To Comcast [Member] 4.00% Notes Due 2049 To Comcast [Member] Other Including Capital Lease Obligations [Member] Other Including Capital Lease Obligations [Member] Other Including Capital Lease Obligations [Member] Foreign Currency Denominated Borrowings [Member] Foreign Currency Denominated Borrowings [Member] Foreign Currency Denominated Borrowings [Member] Commercial paper Commercial Paper Revolving credit facility Long-term Line of Credit Term loans Other Long-term Debt Senior notes Senior Notes Notes due 2049 to Comcast Other Notes Payable, Noncurrent Other, including capital lease obligations Other Borrowings Debt issuance costs, premiums, discounts, fair value adjustments for acquisition accounting and hedged positions, net Debt Issuance Costs, Premiums, Discounts And Fair Value Adjustments For Acquisition Accounting And Hedged Positions Debt Issuance Costs, Premiums, Discounts And Fair Value Adjustments For Acquisition Accounting And Hedged Positions Debt issuance costs, premiums and discounts, net Debt Issuance Costs, Premiums And Discounts, Net The carrying amount as of the balance sheet date for the net impact of debt issuance costs, premiums and discounts. Total debt Debt and Lease Obligation Less: Current portion Interest rate Debt, Weighted Average Interest Rate Aggregate principal amount Debt Instrument, Face Amount Condensed Income Statement [Table] Condensed Income Statement [Table] Service [Member] Service [Member] Management Fee [Member] Management Fee [Member] Management Fee [Member] Condensed Income Statements, Captions [Line Items] Condensed Income Statements, Captions [Line Items] Revenue: Revenues [Abstract] Income tax (expense) benefit Comprehensive income attributable to Comcast Corporation Comprehensive Income (Loss), Net of Tax, Attributable to Parent Long-Term Debt Debt Disclosure [Text Block] Schedule of Equity Method Investments [Table] Schedule of Equity Method Investments [Table] Atairos [Member] Atairos [Member] Atairos [Member] Hulu [Member] Hulu [Member] Hulu member. Title of Individual [Axis] Title of Individual [Axis] Title of Individual [Domain] Title of Individual [Domain] Former CFO [Member] Former CFO [Member] Former CFO [Member] Counterparty Name [Axis] Counterparty Name [Axis] Counterparty Name [Domain] Counterparty Name [Domain] AT&T Inc. [Member] AT&T Inc. [Member] AT&T Inc. [Member] Time Warner, Inc. [Member] Time Warner, Inc. [Member] Time Warner, Inc. [Member] Variable Interest Entities [Axis] Variable Interest Entities [Axis] Variable Interest Entity, Classification [Domain] Variable Interest Entity, Classification [Domain] Variable Interest Entity, Not Primary Beneficiary [Member] Variable Interest Entity, Not Primary Beneficiary [Member] Schedule of Equity Method Investments [Line Items] Schedule of Equity Method Investments [Line Items] Term of agreement Term of agreement Term of agreement for Atairos Funding commitment Equity Method Investment, Funding Commitment Equity Method Investment, Funding Commitment Management fee funding commitment Equity Method Investment, Management Fee Funding Commitment Equity Method Investment, Management Fee Funding Commitment Funding commitment by management company investors Equity Method Investment, Funding Commitment by Management Company Investors Equity Method Investment, Funding Commitment by Management Company Investors Percent of losses Equity Method Investment, Percent of Losses Represents the percentage of any losses in an equity method investment that the Company is obligated to absorb. Percentage of residual returns Percentage of residual returns Represents the percentage of any residual returns that we have the right to receive Unfunded capital commitment Variable Interest Entity, Reporting Entity Involvement, Unfunded Capital Commitment Variable Interest Entity, Reporting Entity Involvement, Unfunded Capital Commitment Equity in net income (losses) of investees, net Cash capital contributions for equity method investments Capital Contribution To VIE The cash outflow associated with a capital contribution to a VIE accounted for as an equity method investment Equity method investments Equity Method Investments Pretax gain, sale of business to Atairos Gain (Loss) on Disposition of Business Ownership percentage Equity Method Investment, Ownership Percentage Cash capital contributions for equity method investments Payments to Acquire Equity Method Investments Maximum total capital call in annual period Equity Method Investment, Maximum Total Capital Call In Annual Period Equity Method Investment, Maximum Total Capital Call In Annual Period Ownership percentage floor Equity Method Investment, Ownership Percentage, Floor Equity Method Investment, Ownership Percentage, Floor Fair market value assessment floor for put and call option Equity Method Investment, Fair Market Value, Floor For Put And Call Option Fair market value floor representing minimum total equity value of investment for put and call option. Ownership percentage representing fair market value floor for put and call option Equity Method Investment, Ownership Percentage Representing Fair Market Value Floor For Put And Call Option Equity Method Investment, Ownership Percentage Representing Fair Market Value Floor For Put And Call Option Minimum guaranteed proceeds floor for put and call option Equity Method Investment, Minimum Guaranteed Proceeds Floor For Put And Call Option Equity Method Investment, Minimum Guaranteed Proceeds Floor Estimated fair value of collateralized obligation Collateralized Obligation, Fair Value Fair value of obligation presented separately as collateralized obligation that is secured by assets. Deferred gain Deferred Gain Recognized On Dilution Of Equity Method Investment Deferred Gain Recognized On Dilution Of Equity Method Investment Revenue Business Acquisition, Pro Forma Revenue Net income attributable to Comcast Corporation Business Acquisition, Pro Forma Net Income (Loss) Attributable To Parent The Pro Forma Net Income (Loss) Attributable To Parent for the period as if the business combination had been completed at the beginning of the period Basic earnings per common share attributable to Comcast Corporation shareholders (in dollars per share) Business Acquisition, Pro Forma Earnings Per Share, Basic Diluted earnings per common share attributable to Comcast Corporation shareholders (in dollars per share) Business Acquisition, Pro Forma Earnings Per Share, Diluted Schedule of Investments [Line Items] Equity method Marketable equity securities Other investments Other Investments Total investments Investments Less: Current investments Short-term Investments Less: Investment securing collateralized obligation Noncurrent investments Distribution System [Member] Distribution System [Member] Distribution System [Member] Other Equipment [Member] Other Capitalized Property Plant and Equipment [Member] Buildings and Leasehold Improvements [Member] Building and Building Improvements [Member] Furniture, Fixtures and Equipment [Member] Furniture and Fixtures [Member] Construction in Process [Member] Construction in Progress [Member] Land [Member] Land [Member] Weighted-Average Original Useful Life Property and equipment, at cost Property, Plant and Equipment, Gross Less: Accumulated depreciation Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Property and equipment, net Other operating and administrative expenses Business Combination, Acquisition Related Costs Interest expense Interest Expenses Financing costs associated with debt facilities and the borrowings related to acquisition. Comcast and NBCUniversal Senior Notes [Member] Comcast and NBCUniversal Senior Notes [Member] Comcast and NBCUniversal Senior Notes [Member] Debt Conversion Description [Axis] Debt Conversion Description [Axis] Debt Conversion, Name [Domain] Debt Conversion, Name [Domain] Senior Notes Exchange [Member] Senior Notes Exchange [Member] Senior Notes Exchange [Member] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Senior Notes [Member] Senior Notes [Member] Universal Beijing Resort [Member] Universal Beijing Resort [Member] Universal Beijing Resort [Member] Capital Costs Incurred But Not Yet Paid Capital Costs Incurred But Not Yet Paid Future cash outflow to pay for purchases of property and equipment and intangible assets that have occurred. Dividends payable Dividends Payable Dividends payable (in dollars per share) Dividends Payable, Amount Per Share Assets contributed to variable interest entity Contribution of Property Aggregate principal amount issued Aggregate principal amount of certain series of outstanding notes Debt Exchange, Amount The aggregate principal amount of the debt being exchanged in a debt exchange transaction. Stock options [Member] Share-based Payment Arrangement, Option [Member] Share-based compensation arrangement by share-based payment award, award vesting period in years Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Period from grant date that an equity-based award expires Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period Unrecognized pretax compensation expense on nonvested awards Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount Unrecognized pretax compensation expense on nonvested awards, weighted average period of recognition (in years) Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition Adjustments to additional paid in capital, income tax benefit from share-based compensation Share-based Payment Arrangement, Expense, Tax Benefit Retirement Benefits [Abstract] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table] Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] Cash surrender value of life insurance policies Cash Surrender Value of Life Insurance Expenses related to retirement investment plans Defined Contribution Plan, Cost Severance costs Other Restructuring Costs Cover page. Document And Entity Information [Table] Document And Entity Information [Table] Document And Entity Information [Table] 2.0% Exchangeable Subordinated Debentures due 2029 [Member] Exchangeable Subordinated Debentures 2.0 Percent Due 2029 [Member] Exchangeable Subordinated Debentures 2.0% Due 2029 [Member] 5.50% Notes due 2029 [Member] Notes 5.50 Percent Due 2029 [Member] Notes 5.50% Due 2029 [Member] 9.455% Guaranteed Notes due 2022 [Member] Guaranteed Notes 9.455 Percent Due 2022 [Member] Guaranteed Notes 9.455% Due 2022 [Member] Document And Entity Information [Line Items] Document And Entity Information [Line Items] [Line Items] for Document And Entity Information [Table] Document Type Document Type Document Fiscal Period Focus Document Fiscal Period Focus Document Annual Report Document Annual Report Document Period End Date Document Period End Date Document Transition Report Document Transition Report Amendment Flag Amendment Flag Document Fiscal Year Focus Document Fiscal Year Focus Current Fiscal Year End Date Current Fiscal Year End Date Entity Central Index Key Entity Central Index Key Entity File Number Entity File Number Entity Registrant Name Entity Registrant Name Entity Tax Identification Number Entity Tax Identification Number Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Entity Address, Address Line One Entity Address, Address Line One Entity Address, City or Town Entity Address, City or Town Entity Address, State or Province Entity Address, State or Province Entity Address, Postal Zip Code Entity Address, Postal Zip Code City Area Code City Area Code Local Phone Number Local Phone Number Title of 12(b) Security Title of 12(b) Security Trading Symbol Trading Symbol Security Exchange Name Security Exchange Name Entity Well-known Seasoned Issuer Entity Well-known Seasoned Issuer Entity Voluntary Filers Entity Voluntary Filers Entity Current Reporting Status Entity Current Reporting Status Entity Interactive Data Current Entity Interactive Data Current Entity Filer Category Entity Filer Category Entity Small Business Entity Small Business Entity Emerging Growth Company Entity Emerging Growth Company Entity Shell Company Entity Shell Company Entity Public Float Entity Public Float Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Documents Incorporated by Reference Documents Incorporated by Reference [Text Block] Statement of Cash Flows [Abstract] Net income Adjustments to reconcile net income to net cash provided by operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Depreciation, amortization and other operating gains Depreciation And Amortization And (Gain) Loss On Disposition Of Assets Depreciation And Amortization Expense And (Gain) Loss on Disposition of Assets Share-based compensation Share-based Payment Arrangement, Noncash Expense Noncash interest expense (income), net Noncash Interest Expense (Income) Net Represents noncash interest expense (income) items as adjustments to reconcile net income (loss) to cash provided by (used in) operating activities. Net (gain) loss on investment activity and other Gain (Loss) On Investments And Other Noncash Income (Loss) Net Net (gain) loss on investment activity, including cash received from investees, and other noncash income (loss), net. Deferred income taxes Changes in operating assets and liabilities, net of effects of acquisitions and divestitures: Increase (Decrease) in Operating Capital [Abstract] Current and noncurrent receivables, net Change In Current And Noncurrent Receivables Net The increase (decrease) during the reporting period in the amount of current and noncurrent receivables. Film and television costs, net Film And Television Costs Net Amount of net increase (decrease) in film and television costs. Accounts payable and accrued expenses related to trade creditors Increase (Decrease) in Accounts Payable and Accrued Liabilities Other operating assets and liabilities Increase (Decrease) in Other Operating Assets and Liabilities, Net Net cash provided by operating activities Note receivable from Comcast Note Receivable Issued From Ultimate Parent Cash flow from note receivable issued from and repayments from Ultimate Parent. Proceeds from (repayments of) borrowings from Comcast, net Proceeds From Note Receivable Issued To And Borrowings From Ultimate Parent Proceeds From Note Receivable Issued To And Borrowings From Ultimate Parent Distributions to member Payments of Capital Distribution Distributions to noncontrolling interests Distributions To Noncontrolling Interest Holders The cash outflow related to distributions to noncontrolling interests. Increase (decrease) in cash, cash equivalents and restricted cash Reconciliation of Adjusted EBITDA from Segments to Consolidated [Table] Reconciliation of Operating Profit (Loss) from Segments to Consolidated [Table] Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] Adjustment for legal settlement Gain (Loss) Related to Litigation Settlement Adjustment for Sky transaction-related costs Transaction Related Costs Acquisition related and integration costs which have been expensed during the period. Such costs could include costs directly related to the transaction, including the U.K. share acquisition tax and success-based investment banker fees, and legal, accounting and valuation services, and costs incurred to effect a business combination, such as business integration costs, systems integration and conversion costs, and severance and other employee-related costs. Depreciation Amortization Other operating gains Interest expense Investment and other income (loss), net Other Industries [Abstract] Film And Television Costs [Table] Film And Television Costs [Table] Film And Television Costs [Table] Film And Television Costs [Line Items] Film And Television Cost [Line Items] [Line Items] for Film And Television Cost [Table] Film and Television Costs Schedule Of Film And Television Costs [Table Text Block] Schedule Of Film And Television Costs [Table Text Block] Weighted average fair value of RSUs (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Stock option fair value (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value Stock Option Valuation Assumptions: Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract] Dividend yield Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate Expected volatility Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate Risk-free interest rate Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate Expected option life Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term Lessee, Lease, Description [Table] Lessee, Lease, Description [Table] Lessee, Lease, Description [Line Items] Lessee, Lease, Description [Line Items] 2020 Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year 2021 Lessee, Operating Lease, Liability, Payments, Due Year Two 2022 Lessee, Operating Lease, Liability, Payments, Due Year Three 2023 Lessee, Operating Lease, Liability, Payments, Due Year Four 2024 Lessee, Operating Lease, Liability, Payments, Due Year Five Thereafter Lessee, Operating Lease, Liability, Payments, Due after Year Five Total future minimum lease payments Lessee, Operating Lease, Liability, Payments, Due Less: imputed interest Lessee, Operating Lease, Liability, Undiscounted Excess Amount Total liability Software [Member] Computer Software, Intangible Asset [Member] Number of divisions Number of Divisions Number of Divisions Finite-lived intangible asset amortization period Schedule of Operating Leased Assets [Table] Schedule of Operating Leased Assets [Table] Operating Leased Assets [Line Items] Operating Leased Assets [Line Items] 2019 Operating Leases, Future Minimum Payments Due, Next Twelve Months 2020 Operating Leases, Future Minimum Payments, Due in Two Years 2021 Operating Leases, Future Minimum Payments, Due in Three Years 2022 Operating Leases, Future Minimum Payments, Due in Four Years 2023 Operating Leases, Future Minimum Payments, Due in Five Years Thereafter Operating Leases, Future Minimum Payments, Due Thereafter SEC Schedule, 12-09, Valuation Allowances and Reserves Type [Axis] SEC Schedule, 12-09, Valuation Allowances and Reserves Type [Axis] SEC Schedule, 12-09, Valuation Allowances and Reserves [Domain] SEC Schedule, 12-09, Valuation Allowances and Reserves [Domain] Allowance for doubtful accounts [Member] SEC Schedule, 12-09, Allowance, Credit Loss [Member] Valuation allowance on deferred tax assets [Member] SEC Schedule, 12-09, Valuation Allowance, Deferred Tax Asset [Member] SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] Balance at Beginning of Year SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount Additions Charged to Costs and Expenses SEC Schedule, 12-09, Valuation Allowances and Reserves, Additions, Charge to Cost and Expense Deductions from Reserves SEC Schedule, 12-09, Valuation Allowances and Reserves, Deduction Balance at End of Year Condensed Balance Sheet Statement [Table] Condensed Balance Sheet Statement [Table] Condensed Balance Sheet Statements, Captions [Line Items] Condensed Balance Sheet Statements, Captions [Line Items] Investments in and amounts due from subsidiaries eliminated upon consolidation Investments In And Amounts Due From Subsidiaries Eliminated Upon Consolidation Investments in and amounts due from subsidiaries eliminated upon consolidation Redeemable noncontrolling interests and redeemable subsidiary preferred stock Common stock Other shareholders’ equity Other stockholders equity Other stockholders equity. Deferred Compensation Plans [Member] Deferred Compensation Plans [Member] Deferred Compensation Plans [Member] Benefit obligation Deferred Compensation Plans Benefit Obligation Deferred compensation plans benefit obligation Interest expense Deferred Compensation Plans interest cost Deferred compensation plans interest cost Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Condensed Consolidated Balance Sheet [Line Items] Accounts, Notes, Loans and Financing Receivable [Line Items] Receivables, gross Accounts Receivable, before Allowance for Credit Loss, Current Less: Allowance for doubtful accounts Accounts Receivable, Allowance for Credit Loss, Current Receivables, net Noncurrent receivables (included in other noncurrent assets, net) Accounts Receivable, after Allowance for Credit Loss, Noncurrent Contract acquisition and fulfillment costs (included in other noncurrent assets, net) Capitalized Contract Cost, Net Noncurrent deferred revenue (included in other noncurrent liabilities) Deferred Revenue, Noncurrent Investments [Table] Investments [Table] Investments [Table] Investments [Line Items] Investments [Line Items] [Line Items] for Investments [Table] Investment and Other Income (Loss), Net Components Of Investment and Other Income Loss Net [Table Text Block] Tabular disclosure of investment and other income (loss), net, including, but not limited to, equity in net income (losses) of investees, net, realized and unrealized gains (losses) on equity securities, net, and other income (loss), net. Investment Summary Summary Investment Holdings [Table Text Block] Employee stock purchase plans [Member] Employee Stock [Member] Recognized share-based compensation expense Share-based Payment Arrangement, Expense Geographical [Axis] Geographical [Axis] Geographical [Domain] Geographical [Domain] United States [Member] UNITED STATES Europe [Member] Europe [Member] Other [Member] Other Geographic Locations [Member] Other Geographic Locations [Member] Foreign [Member] Non-US [Member] Disaggregation of Revenue [Line Items] Schedule of Variable Interest Entities [Table] Schedule of Variable Interest Entities [Table] Ownership [Axis] Ownership [Axis] Ownership [Domain] Ownership [Domain] Universal Beijing Resort Term Loans [Member] Universal Beijing Resort Term Loans [Member] Universal Beijing Resort Term Loans [Member] Variable Interest Entity, Primary Beneficiary [Member] Variable Interest Entity, Primary Beneficiary [Member] Variable Interest Entity [Line Items] Variable Interest Entity [Line Items] Ownership percentage in variable interest entity Noncontrolling Interest, Ownership Percentage by Parent Maximum borrowing capacity of variable interest entity Variable Interest Entity, Maximum Borrowing Capacity Variable interest entity, maximum borrowing capacity under financing agreements. Proceeds from borrowings Consolidated variable interest entity's assets included in condensed consolidated balance sheet Variable Interest Entity, Consolidated, Carrying Amount, Assets Consolidated variable interest entity's liabilities included in condensed consolidated balance sheet Variable Interest Entity, Consolidated, Carrying Amount, Liabilities Significant Transactions Significant Transactions [Text Block] The disclosure of significant transactions entered into or completed during the period. Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Domain] Concentration Risk Benchmark [Domain] Workforce Subject to Collective Bargaining Arrangements [Member] Workforce Subject to Collective Bargaining Arrangements [Member] Workforce Subject to Collective Bargaining Arrangements Expiring within One Year [Member] Workforce Subject to Collective Bargaining Arrangements Expiring within One Year [Member] NBCUniversal Enterprise [Member] NBCUniversal Enterprise [Member] Redeemable Subsidiary Preferred Stock [Member] Redeemable Preferred Stock [Member] Number of employees covered under collective bargaining agreements Number Of Employees Covered Under Collective Bargaining Agreements Number of employees covered by collective bargaining agreements. Percentage of full-time equivalent employees covered by collective bargaining agreements that have expired or are schedule to expire during the next year Concentration Risk, Percentage Operating lease expense inclusive of short-term and variable lease expenses Operating Lease Expense Inclusive Of Short Term And Variable Lease Expenses Amount of operating lease expense, inclusive of short-term and variable lease expenses, recognized in our consolidated statement of income. Excludes lease costs associated with production activities or other amounts capitalized in our consolidated balance sheet. Weighted average remaining lease term for operating leases Operating Lease, Weighted Average Remaining Lease Term Weighted average discount rate used to calculate operating lease liabilities Operating Lease, Weighted Average Discount Rate, Percent Cash payments for operating leases Operating Lease, Payments Future cash payments related to additional contracts determined to be operating leases Additional Operating Leases, Future Minimum Payments Due Amount of required minimum rental payments for leases having an initial or remaining non-cancelable letter-terms in excess of one year related to additional contracts determined to be operating leases in connection with the business acquisition. Carrying value of contractual obligation Carrying value of contractual obligation Carrying value of future obligation classified as a liability which is no longer recorded at fair value. Contractual value of a potential obligation Contractual Value of a Potential Future Obligation Contractual value of a potential future obligation based on a contractual formula on a specified date. Redeemable subsidiary preferred stock, put period Preferred Stock, Put Period The holders have the right to cause the issuing company to redeem their shares at a price equal to the liquidation preference plus accrued but unpaid dividends for a 30 day period beginning on March 19, 2020 and thereafter on every third anniversary of such date (each such date, a “put date”). Redeemable subsidiary preferred stock, dividend rate Preferred Stock, Dividend Rate, Percentage Redeemable subsidiary preferred stock, call period Preferred Stock, Call Period Shares of preferred stock can be called for redemption by the issuing company at a price equal to the liquidation preference plus accrued but unpaid dividends one year following the put date applicable to such shares. Temporary equity, fair value of redeemable subsidiary preferred stock Temporary Equity, Fair Value Of Redeemable Subsidiary Preferred Stock Temporary Equity, Fair Value of our redeemable subsidiary preferred stock. Residential, High-Speed Internet [Member] Residential, High-Speed Internet [Member] Residential, High-Speed Internet [Member] Residential, Video [Member] Residential, Video [Member] Residential, Video [Member] Residential, Voice [Member] Residential, Voice [Member] Residential, Voice [Member] Residential, Wireless [Member] Residential, Wireless [Member] Residential, Wireless [Member] Content Licensing And Other [Member] Content Licensing And Other [Member] Content Licensing And Other [Member] Content [Member] Content [Member] Content [Member] Distribution And Other [Member] Distribution And Other [Member] Distribution And Other [Member] Other [Member] Other [Member] Other [Member] Franchise And Other Regulatory Fees [Member] Franchise And Other Regulatory Fees [Member] Franchise And Other Regulatory Fees [Member] Cable segment revenue types as percentage of total cable revenue Cable Segment Revenue Types As Percentage Of Total Cable Revenue Cable segment revenue types as percentage of total cable revenue Domestic Income (Loss) from Continuing Operations before Income Taxes, Domestic Foreign Income (Loss) from Continuing Operations before Income Taxes, Foreign Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward] Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward] Gross unrecognized tax benefits, January 1 Unrecognized Tax Benefits Additions based on tax positions related to the current year Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions Additions based on tax positions related to prior years Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions Additions from acquired subsidiaries Unrecognized Tax Benefits Increases Resulting From Acquired Subsidiaries Unrecognized Tax Benefits Increases Resulting From Acquired Subsidiaries Reductions for tax positions of prior years Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions Reductions due to expiration of statutes of limitations Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations Settlements with tax authorities Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities Gross unrecognized tax benefits, December 31 Positions paid Unrecognized Tax Benefits Positions Paid Unrecognized tax benefits associated with positions for which tax has been assessed and paid. Related Party Transactions Related Party Transactions Disclosure [Text Block] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Other noncurrent assets, net Other Noncurrent Assets [Member] Accrued expenses and other current liabilities Accrued Liabilities [Member] Other noncurrent liabilities Other Noncurrent Liabilities [Member] Operating lease liabilities, current Operating Lease, Liability, Current Operating lease liabilities, noncurrent Operating Lease, Liability, Noncurrent Related Party Transactions Condensed Financial Statements Schedule of Related Party Transactions [Table Text Block] Condensed Consolidating Financial Information Condensed Financial Information of Parent Company Only Disclosure [Text Block] Deferred Compensation Plans Deferred Compensation Plans [Table Text Block] Information regarding deferred compensation plans, including benefit obligations and related expense. Programming and Talent Commitments [Line Items] 2020 Contractual Obligation, Due in Next Fiscal Year 2021 Contractual Obligation, Due in Second Year 2022 Contractual Obligation, Due in Third Year 2023 Contractual Obligation, Due in Fourth Year 2024 Contractual Obligation, Due in Fifth Year Thereafter Contractual Obligation, Due after Fifth Year Equity Stockholders' Equity Note Disclosure [Text Block] Schedule of Finite-Lived Intangible Assets [Table] Schedule of Finite-Lived Intangible Assets [Table] Estimated Amortization Expense of Finite-Lived Intangible Assets Finite-Lived Intangible Assets [Line Items] 2020 Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months 2021 Finite-Lived Intangible Assets, Amortization Expense, Year Two 2022 Finite-Lived Intangible Assets, Amortization Expense, Year Three 2023 Finite-Lived Intangible Assets, Amortization Expense, Year Four 2024 Finite-Lived Intangible Assets, Amortization Expense, Year Five Investments Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Hedging Relationship [Axis] Hedging Relationship [Axis] Hedging Relationship [Domain] Hedging Relationship [Domain] Cash Flow Hedging [Member] Cash Flow Hedging [Member] Net Investment Hedging [Member] Net Investment Hedging [Member] Derivative Instrument [Axis] Derivative Instrument [Axis] Derivative Contract [Domain] Derivative Contract [Domain] Currency Swap [Member] Currency Swap [Member] Financial Instrument [Axis] Financial Instrument [Axis] Financial Instruments [Domain] Financial Instruments [Domain] Currency Swaps And Foreign Currency Denominated Debt [Member] Currency Swaps And Foreign Currency Denominated Debt [Member] Currency Swaps And Foreign Currency Denominated Debt [Member] Credit Facility [Axis] Credit Facility [Axis] Credit Facility [Domain] Credit Facility [Domain] Comcast Revolving Credit Facility due 2022 [Member] Comcast Revolving Credit Facility due 2022 [Member] Sky Revolving Credit Facility [Member] Sky Revolving Credit Facility [Member] Sky Revolving Credit Facility [Member] Comcast, Comcast Cable And NBCUniversal Debt Securities [Member] Comcast, Comcast Cable And NBCUniversal Debt Securities [Member] Comcast, Comcast Cable And NBCUniversal Debt Securities [Member] Comcast And Comcast Cable Debt Securities [Member] Comcast And Comcast Cable Debt Securities [Member] NBCUniversal Enterprise Debt Securities [Member] NBCUniversal Enterprise Debt Securities [Member] NBCUniversal Enterprise Debt Securities [Member] Universal Studios Japan Term Loans [Member] Universal Studios Japan Term Loans [Member] Universal Studios Japan Term Loans [Member] Sky Debt Securities [Member] Sky Debt Securities [Member] Sky Debt Securities [Member] Variable Rate [Axis] Variable Rate [Axis] Variable Rate [Domain] Variable Rate [Domain] London Interbank Offered Rate (LIBOR) [Member] London Interbank Offered Rate (LIBOR) [Member] Total fair value of debt Long-term Debt, Fair Value Amount of foreign currency denominated debt hedged Amount Of Foreign Currency Denominated Debt Hedged Amount of foreign currency denominated debt that has been hedged. Aggregate asset (liability) fair value Derivative Assets (Liabilities), at Fair Value, Net Amount of net investment in foreign subsidiaries hedged Amount Of Net Investment In Foreign Subsidiaries Hedged Aggregate amount of net investment in foreign subsidiaries that has been hedged. Cumulative translation gains (losses) related to net investment hedges recorded in AOCI Maximum borrowing capacity of revolving credit facilities Line of Credit Facility, Maximum Borrowing Capacity Potential increase of maximum borrowing capacity of revolving credit facilities Line of Credit facility, Potential increase to Maximum Borrowing Capacity Potential increased maximum borrowing capacity under the revolving credit facility, subject to approval of the lenders. Borrowing margin for LIBOR based borrowings Debt Instrument, Basis Spread on Variable Rate Amounts available under revolving credit facilities Line of Credit Facility, Remaining Borrowing Capacity Net repayments of credit facility Proceeds from (Repayments of) Lines of Credit Credit facility terminated Line Of Credit Facility, Borrowing Capacity Of Credit Facility Terminated Line Of Credit Facility, Borrowing Capacity Of Credit Facility Terminated Unused irrevocable standby letters of credit and bank guarantees Letters Of Credit And Bank Guarantees, Outstanding Amount The total amount of the contingent obligation under letters of credit outstanding and our bank guarantees as of the reporting date. Ownership in cable holding company subsidiaries Ownership In Cable Holding Company Subsidiaries Represents the Company's ownership in its cable holding company subsidiaries. Principal amount of debt securities subject to guarantee Guarantee Obligations, Debt Securities Principal amount of debt securities subject to guarantee. Principal amount of debt securities subject to guarantee maturing within the next 5 years Guarantee Obligations, Debt Securities, Maturing Within Five Years Guarantee Obligations, Debt Securities, Maturing Within Five Years Guarantee obligations, maximum capacity of credit facility Guarantee Obligations Maximum Capacity Of Credit Facility Maximum capacity of credit facility subject to cross-guarantee Related party aggregate principal amount senior notes not subject to guarantee Related Party, Aggregate Debt Securities, Not Subject To Guarantee Represents the related party aggregate principal amount of debt securities not subject to guarantee. Related party liquidation preference preferred stock not subject to guarantee Related Party Liquidation Preference Preferred Stock Not Subject To Guarantee Represents the related party liquidation preference of preferred stock not subject to guarantee. Allocation of Purchase Price Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block] Amounts Related to Expenses Included in Consolidated Statement of Operations Schedule of Business Acquisitions, by Acquisition [Table Text Block] Unaudited Pro Forma Information Business Acquisition, Pro Forma Information [Table Text Block] Film Costs: Theatrical Film Costs [Abstract] Released, less amortization Theatrical Film Costs, Released Completed, not released Theatrical Film Costs, Completed and Not Released In production and in development Theatrical Film Costs, In Production And In Development The amount of direct negative costs incurred in the production and development of a theatrical film, as well as allocations of production overhead and capitalized interest. Examples of direct negative costs include costs of story and scenario; compensation of cast, directors, producers, extras, and miscellaneous staff; costs of set construction and operations, wardrobe, and accessories; costs of sound synchronization; rental facilities on location; and postproduction costs such as music, special effects, and editing. Total film costs Theatrical Film Costs Television Costs: Direct-to-television Film Costs [Abstract] Released, less amortization Direct-to-television Film Costs, Released In production and in development Direct-to-Television Film Costs, In Production and In Development The amount of direct negative costs incurred in the production and development of a direct-to-television film, as well as allocations of production overhead and capitalized interest. Examples of direct negative costs include costs of story and scenario; compensation of cast, directors, producers, extras, and miscellaneous staff; costs of set construction and operations, wardrobe, and accessories; costs of sound synchronization; rental facilities on location; and postproduction costs such as music, special effects, and editing. Total television costs Direct-to-television Film Costs Programming rights, less amortization Programming Rights Less Amortization The carrying amount of total acquired programming rights, less amortization Total film costs, television costs and programming rights Total Film And Television Costs And Programming Rights After Amortization The carrying amount of owned films, television series and other television productions and the current and noncurrent portion of acquired television and cable networks programming rights recorded on the balance sheet. Owned films, television series and other television production costs include capitalizable production costs, production overhead, interest, development costs and acquired production costs. Film and television rights include multi-year programming arrangements, acquired movies, series and other programs. The carrying amount is stated at the lower of cost, less accumulated amortization, or net realizable/fair value at the balance sheet date. Less: Current portion of programming rights Related Party Transaction [Axis] Related Party Transaction [Axis] Related Party Transaction [Domain] Related Party Transaction [Domain] Non-Interest Bearing Notes Due 2024 [Member] Non-Interest Bearing Notes Due 2024 [Member] Non-Interest Bearing Notes Due 2024 [Member] Comcast And NBCUniveral Revolving Credit Agreements [Member] Comcast And NBCUniveral Revolving Credit Agreements [Member] Comcast And NBCUniveral Revolving Credit Agreements [Member] Notes Payable [Member] Notes Payable, Other Payables [Member] 4.00% Notes Due 2049 [Member] 4.00% Notes Due 2049 [Member] 4.00% Notes Due 2049 [Member] Senior 6.40% Notes Due 2040 [Member] Senior 6.40% Notes Due 2040 [Member] Senior 6.400% Notes Due 2040 [Member] Carrying Value Of Related Party Contractual Obligation [Member] Carrying Value Of Related Party Contractual Obligation [Member] NBCUniversal Holdings Preferred Stock [Member] NBCUniversal Holdings Preferred Stock [Member] Comcast and NBCUniversal Revolving Credit Agreements [Member] Comcast and NBCUniversal Revolving Credit Agreements [Member] Comcast and NBCUniversal Revolving Credit Agreements [Member] Revolving credit agreement capacity Revolving Credit Agreement Capacity The maximum amount of borrowing or lending capacity including the cash management arrangement between ultimate parent and subsidiary under the matching revolving credit facilities. Repayments of debt Repayment Of Notes Payable To Ultimate Parent Repayment to ultimate parent including cash management arrangement under the matching revolving credit facilities. Repayments of Debt Interest rate Debt Instrument, Interest Rate, Stated Percentage Gain (loss) on extinguishment of debt Gain (Loss) on Extinguishment of Debt Amount of debt exchanged Preferred stock, dividend rate Preferred stock liquidation preference value Preferred Stock, Liquidation Preference, Value Preferred stock dividend rate, spread on variable rate Preferred Stock Dividend Rate, Spread On Variable Rate Percentage points added to the reference rate to compute the variable rate on dividend payments on preferred stock; the variable rate will reset every 5 years Schedule of common stock outstanding Schedule of Common Stock Outstanding Roll Forward [Table Text Block] Schedule of shares repurchased Class of Treasury Stock [Table Text Block] Recent Accounting Pronouncements New Accounting Pronouncements and Changes in Accounting Principles [Text Block] Consideration transferred Cash Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents Accounts receivable and other current assets Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Accounts Receivable And Other Current Assets Amount of accounts receivable and other current assets recognized as of the acquisition date. Film and television costs (See Note 4) Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Film And Television Costs Amount of Film And Television Costs recognized as of the acquisition date Property and equipment (See Note 11) Intangible assets (See Note 12) Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill Accounts payable, accrued liabilities and other current liabilities Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Accounts Payable, Accrued Liabilities, And Other Current Liabilities Amount of accounts payable, accrued liabilities, and other current liabilities recognized as of the acquisition date. Long-term debt (See Note 7) Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt Deferred tax assets (liabilities), net (See Note 5) Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Assets (Liabilities), Net Amount of Deferred Tax Assets (Liabilities), Net recognized as of the acquisition date Other noncurrent assets and (liabilities), net Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets And Liabilities, Net Amount of Other Noncurrent Assets And Liabilities, Net recognized as of the acquisition date Fair value of identifiable net assets acquired Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net Financial Data by Business Segment Schedule of Segment Reporting Information, by Segment [Table Text Block] Reconciliation of Adjusted EBITDA from Segments to Consolidated Reconciliation of Operating Profit (Loss) from Segments to Consolidated [Table Text Block] Property and Equipment Property, Plant and Equipment [Table Text Block] Basic EPS attributable to Comcast Corporation shareholders (in shares) Weighted Average Number of Shares Outstanding, Basic Effect of dilutive securities: Dilutive Securities, Effect on Basic Earnings Per Share [Abstract] Assumed exercise or issuance of shares relating to stock plans (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Diluted EPS attributable to Comcast Corporation shareholders (in shares) Weighted Average Number of Shares Outstanding, Diluted Restricted cash included in other current assets Restricted Cash, Current Restricted cash included in other noncurrent assets, net Restricted Cash, Noncurrent Cash, cash equivalents and restricted cash, end of year Amortization of completed film and television production expected to be amortized during the next fiscal year Film Costs, Amortized in Next Operating Cycle Expected amortization percentage of released and unamortized film and television costs during the next three fiscal years Percentage of Unamortized Film Costs Remaining unamortized costs of acquired film and television libraries Film And Television Library Costs Unamortized The remaining amount of costs related to film and television libraries that are expected to be amortized. Amortization period of acquired film and television library costs Acquired Film and Television Library Costs, Amortization Period Acquired Film and Television Library Costs, Amortization Period Expected amortization percentage of unamortized acquired film and television library costs during the next three fiscal years Percentage Of Acquired Film And Television Libraries To Be Amortized In The Next Three Years The percentage of unamortized acquired film and television library costs that are expected to be amortized within three years from the date of the balance sheet. Basis of Presentation and Summary of Significant Accounting Policies Business Description and Basis of Presentation [Text Block] Quarterly Financial Information (Unaudited) Quarterly Financial Information [Text Block] Employee Benefit Plans Pension and Other Postretirement Benefits Disclosure [Text Block] Income Taxes Income Tax Disclosure [Text Block] Unrealized gains (losses) on marketable securities, net of deferred taxes Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, after Tax Deferred gains (losses) on cash flow hedges, net of deferred taxes Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification, after Tax Amounts reclassified to net income: Amounts Reclassified To Net Income [Abstract] Realized (gains) losses on marketable securities, net of deferred taxes Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax Realized (gains) losses on cash flow hedges, net of deferred taxes Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax Employee benefit obligations, net of deferred taxes Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax Currency translation adjustments, net of deferred taxes Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax Comprehensive income Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Less: Net income attributable to noncontrolling interests and redeemable subsidiary preferred stock Less: Net income attributable to noncontrolling interests Less: Other comprehensive income (loss) attributable to noncontrolling interests Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest Schedule of recognized share-based compensation expense Share-based Payment Arrangement, Cost by Plan [Table Text Block] Schedule of stock option and restricted share units activity Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block] Schedule of stock option and restricted share units fair value and significant assumptions Stock Option Fair Value and Significant Assumptions [Text Block] Stock option fair value and significant assumptions Programming and Production Costs Film And Television Costs Disclosure [Text Block] Film and Television costs Disclosure [Text Block] Schedule of Indefinite and Finite-Lived Intangible Assets [Table] Schedule of Indefinite and Finite-Lived Intangible Assets [Table] Schedule of assets, excluding financial assets and goodwill, lacking physical substance. Schedule of Indefinite and Finite-Lived Intangible Assets [Line Items] Schedule of Indefinite and Finite-Lived Intangible Assets [Line Items] [Line Items] for Schedule of assets, excluding financial assets and goodwill, lacking physical substance. Total Intangible Assets, Gross (Excluding Goodwill) Schedule of Indefinite-Lived Intangible Assets [Table] Schedule of Indefinite-Lived Intangible Assets [Table] Franchise Rights [Member] Franchise Rights [Member] FCC Licenses [Member] Indefinite-lived Intangible Assets [Line Items] Indefinite-lived Intangible Assets [Line Items] Gross Carrying Amount Other Agreements and Rights [Member] Other Intangible Assets [Member] Weighted-Average Original Useful Life Gross Carrying Amount Finite-Lived Intangible Assets, Gross Accumulated Amortization Finite-Lived Intangible Assets, Accumulated Amortization