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] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] NBCUniversal Media LLC [Member] NBCUniversal Media LLC [Member] NBCUniversal Media LLC [Member] Condensed Consolidated Financial Statements [Line Items] Business And Basis Of Presentation [Line Items] Business And Basis Of Presentation Condensed Consolidated Financial Statements Business Description and Basis of Presentation [Text Block] Investments [Abstract] Schedule of Equity Method Investments [Table] Schedule of Equity Method Investments [Table] Investment, Name [Axis] Investment, Name [Axis] Investment, Name [Domain] Investment, Name [Domain] Atairos [Member] Atairos [Member] Atairos [Member] Hulu [Member] Hulu [Member] Hulu member. The Weather Channel [Member] The Weather Channel [Member] The Weather Channel [Member] Schedule of Equity Method Investments [Line Items] Schedule of Equity Method Investments [Line Items] Funding commitment Equity Method Investment, Funding Commitment Equity Method Investment, Funding Commitment Equity method investments Equity Method Investments Purchases of investments Capital Contribution To VIE The cash outflow associated with a capital contribution to a VIE accounted for as an equity method investment Equity in net income (losses) of investees, net Income (Loss) from Equity Method Investments Cash capital contribution, equity method investment Equity Method Investment, Capital Contribution Equity Method Investment, Capital Contribution Pretax gain on sale of investment Equity Method Investment, Realized Gain (Loss) on Disposal Document and Entity Information [Abstract] DocumentAndEntityInformationAbstract Document And Entity Information [Table] Document And Entity Information [Table] Document And Entity Information [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] Document And Entity Information [Line Items] Document And Entity Information [Line Items] [Line Items] for Document And Entity Information [Table] Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Trading Symbol Trading Symbol Current Fiscal Year End Date Current Fiscal Year End Date Entity Filer Category Entity Filer Category Document Type Document Type Document Period End Date Document Period End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Amendment Flag Amendment Flag Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Accounting Changes and Error Corrections [Abstract] New Accounting Pronouncements or Change in Accounting Principle [Table] New Accounting Pronouncements or Change in Accounting Principle [Table] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Member's Capital [Member] Member's Capital [Member] AOCI Attributable to Parent [Member] AOCI Attributable to Parent [Member] Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] Accounting Standards Update 2016-01 [Member] Accounting Standards Update 2016-01 [Member] Scenario [Axis] Scenario [Axis] Scenario, Unspecified [Domain] Scenario, Unspecified [Domain] Previous Reported [Member] Scenario, Previously Reported [Member] Effects of Adoption [Member] Restatement Adjustment [Member] New Accounting Pronouncements or Change in Accounting Principle [Line Items] New Accounting Pronouncements or Change in Accounting Principle [Line Items] Cumulative Effect of New Accounting Principle in Period of Adoption Cumulative Effect of New Accounting Principle in Period of Adoption Income tax benefit, 2017 tax reform legislation Income Tax Benefit 2017 Tax Reform Legislation Income tax benefit as a result of the 2017 tax reform legislation Income tax benefit, 2018 tax reform legislation Income Tax Benefit, 2018 Tax Reform Legislation Income tax benefit as a result of the 2018 tax reform legislation Debt Disclosure [Abstract] Line of Credit Facility [Table] Line of Credit Facility [Table] Credit Facility [Axis] Credit Facility [Axis] Credit Facility [Domain] Credit Facility [Domain] Revolving Credit Facility [Member] Revolving Credit Facility [Member] NBCUniversal Enterprise [Member] NBCUniversal Enterprise [Member] Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] Amounts available under revolving credit facilities Line of Credit Facility, Remaining Borrowing Capacity Statement of Financial Position [Abstract] Statement [Table] Statement [Table] Statement [Line Items] Statement [Line Items] Assets Assets [Abstract] Current Assets: Assets, Current [Abstract] Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Receivables, net Accounts Receivable, Net, 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. 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 Property and equipment, net Property, Plant and Equipment, Net Franchise rights Indefinite-Lived Franchise Rights Goodwill Goodwill Other intangible assets, net Other Intangible Assets, Net Intangible assets, net Intangible Assets, Net (Excluding Goodwill) 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 Note 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 Capital Lease Obligations 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 (Note 11) Commitments and Contingencies Redeemable noncontrolling interests Redeemable Noncontrolling Interest, Equity, Carrying Amount Equity: Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Preferred stock—authorized, 20,000,000 shares; issued, zero Preferred Stock, Value, Issued 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 Member’s capital Members' Capital Accumulated other comprehensive income (loss) Accumulated Other Comprehensive Income (Loss), Net of Tax 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 Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Total equity Limited Liability Company (LLC) Members' Equity, Including Portion Attributable to Noncontrolling Interest Total liabilities and equity Liabilities and Equity Condensed Financial Information of Parent Company Only Disclosure [Abstract] Condensed Financial Statements [Table] Condensed Financial Statements [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] Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Reportable Legal Entities [Member] Reportable Legal Entities [Member] Elimination and Consolidation Adjustments [Member] Consolidation, Eliminations [Member] Condensed Financial Statements, Captions [Line Items] Condensed Financial Statements, Captions [Line Items] Net Cash Provided by (Used in) Operating Activities [Abstract] Net Cash Provided by (Used in) Operating Activities [Abstract] Net cash provided by 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. Acquisitions, net of cash acquired Payments to Acquire Businesses, Net of Cash Acquired Proceeds from sales of 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 Repurchases and repayments of debt Repayments of Other Debt Repurchases of common stock under repurchase program and employee plans Payments for Repurchase of Common Stock Dividends paid Payments of Dividends 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 Increase (decrease) in cash, 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 period Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Cash, cash equivalents and restricted cash, end of period Accounting Policies [Line Items] Basis of Presentation Basis of Accounting, Policy [Policy Text Block] Revenue Recognition Revenue Recognition, Policy [Policy Text Block] Recent Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Investments Investment, Policy [Policy Text Block] Schedule of Short-term Debt [Table] Schedule of Short-term Debt [Table] Commercial Paper [Member] Commercial Paper [Member] Short-term Debt [Line Items] Short-term Debt [Line Items] Commercial paper outstanding Commercial Paper Share-based Compensation [Abstract] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Plan Name [Axis] Plan Name [Axis] Plan Name [Domain] Plan Name [Domain] Management Grant [Member] Management Grant [Member] Management Grant [Member] Award Type [Axis] Award Type [Axis] Equity Award [Domain] Equity Award [Domain] Restricted share units [Member] Restricted Stock Units (RSUs) [Member] Stock options [Member] Employee Stock Option [Member] Employee Stock purchase plans [Member] Employee Stock [Member] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Number of restricted share units granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Number of stock options granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross Weighted average fair value of restricted share units granted (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 Weighted average fair value of stock options granted (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value Recognized share-based compensation expense Allocated Share-based Compensation Expense Unrecognized pretax compensation expense on nonvested awards Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized Other Industries [Abstract] Film And Television Cost [Table] Film And Television Cost [Table] Film And Television Cost [Table] Film And Television Cost [Line Items] Film And Television Cost [Line Items] [Line Items] for Film And Television Cost [Table] Film And Television Costs Film And Television Costs Disclosure [Text Block] Film and Television costs Disclosure [Text Block] Business Combinations [Abstract] Schedule of Variable Interest Entities [Table] Schedule of Variable Interest Entities [Table] Variable Interest Entities [Axis] Variable Interest Entities [Axis] Variable Interest Entity [Domain] Variable Interest Entity, Classification [Domain] Universal Beijing Resort [Member] Universal Beijing Resort [Member] Universal Beijing Resort [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. 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 Property and equipment - accumulated depreciation Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Other intangible assets - accumulated amortization Finite-Lived Intangible Assets, Accumulated Amortization 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 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] Film and Television Costs Schedule Of Film And Television Costs [Table Text Block] Schedule Of Film And Television Costs [Table Text Block] Debt Securities, Trading, and Equity Securities, FV-NI [Table] 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 Securities, Trading, and Equity Securities, FV-NI [Line Items] [Line Items] for Debt Securities, Trading, and Equity Securities, FV-NI [Table] Realized and unrealized gains (losses) on equity securities, net EquitySecuritiesFvNiGainLoss Amount of unrealized and realized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). 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 Nonoperating Income (Expense) Schedule of Investments [Line Items] Equity method Marketable equity securities Equity Securities, FV-NI Equity Securities, FV-NI Nonmarketable equity securities Equity Securities Without Readily Determinable Fair Value, Amount Amount of investment in equity security without readily determinable fair value. Other investments Other Investments Total investments Investments Less: Current investments Short-term Investments Noncurrent investments Revenue from Contract with Customer [Abstract] Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Geographical [Axis] Geographical [Axis] Geographical [Domain] Geographical [Domain] United States UNITED STATES Foreign Non-US [Member] Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Revenue Revenues Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] NBCUniversal Enterprise Senior Debt Securities [Member] Senior Notes [Member] NBCUniversal Enterprise Credit Facility [Member] NBCUniversal Enterprise Credit Facility [Member] Universal Studios Japan Term Loan Maturing March 2022 [Member] Universal Studios Japan Term Loan Maturing March 2022 [Member] Universal Studios Japan Term Loan Maturing March 2022 [Member] Comcast Holdings' ZONES due October 2029 [Member] Comcast Holdings' ZONES due October 2029 [Member] Comcast Holdings' ZONES due October 2029 [Member] Comcast Holdings' ZONES due November 2029 [Member] Comcast Holdings' ZONES due November 2029 [Member] Comcast Holdings' ZONES due November 2029 Debt Instrument [Line Items] Debt Instrument [Line Items] Principal amount of debt securities subject to guarantee Guarantee Obligations Current Principal Balance Principal amount of debt securities subject to guarantee. Revolving credit facility subject to guarantee Guarantee Obligations, Line Of Credit Facility Guarantee Obligations, Line Of Credit Facility Term loans subject to guarantee Guarantee Obligations, Term Loans Guarantee Obligations, Term Loans Principal amount of debt securities not subject to guarantee Non Guarantee Obligations Current Principal Balance Principal amount of debt instruments not guaranteed by Comcast Corporation, the cable guarantors nor NBCUniversal Media, LLC. Investments [Table] Investments [Table] Investments [Table] Investments [Line Items] Investments [Line Items] [Line Items] for Investments [Table] Investment Summary Summary Investment Holdings [Table Text Block] 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. Segment Reporting [Abstract] Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] 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] Schedule of Other Investments [Table] Schedule of Cost-method Investments [Table] AirTouch [Member] Air Touch [Member] Air Touch [member] Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Fair Value Hierarchy [Domain] Fair Value Hierarchy [Domain] Level 2 [Member] Fair Value, Inputs, Level 2 [Member] AirTouch [Member] Schedule of Other Investments [Line Items] Schedule of Cost-method Investments [Line Items] Number of series of preferred stock Number of Preferred Stock Series Number of Preferred Stock Series Held to maturity investment Held-to-maturity Securities, Noncurrent Fair value of redeemable preferred shares Fair Value Of Redeemable Preferred Shares Fair value of our redeemable subsidiary preferred shares and/or stock Fair value of held to maturity investment redeemable preferred shares Held-to-maturity Securities, Fair Value Operating Segments [Member] Operating Segments [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 Products and Services [Axis] Products and Services [Axis] Products and Services [Domain] Products and Services [Domain] Residential [Member] Residential [Member] Residential [Member] Distribution [Member] Distribution [Member] Distribution Franchise And Other Regulatory Fees [Member] Franchise And Other Regulatory Fees [Member] Franchise And Other Regulatory Fees [Member] Business Services [Member] Business Services [Member] Business Services [Member] Advertising [Member] 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] Range [Axis] Range [Axis] Range [Domain] Range [Domain] Minimum [Member] Minimum [Member] Maximum [Member] Maximum [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 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 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 Condensed Consolidating Financial Information Condensed Financial Information of Parent Company Only Disclosure [Text Block] Accounting Standards Update 2014-09 [Member] Accounting Standards Update 2014-09 [Member] Residential, Video [Member] Residential, Video [Member] Residential, Video [Member] Residential, High-Speed Internet [Member] Residential, High-Speed Internet [Member] Residential, High-Speed Internet [Member] Residential, Voice [Member] Residential, Voice [Member] Residential, Voice [Member] Other [Member] Other [Member] Other [Member] Total costs and expenses Costs and Expenses Depreciation and Amortization Depreciation, Depletion and Amortization, Nonproduction Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent Event [Member] Subsequent Event [Member] Business Acquisition [Axis] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Sky PLC [Member] Sky PLC [Member] Sky Plc [Member] Business Acquisition [Line Items] Business Acquisition [Line Items] Cash offer price per share (in gbp per share) Business Acquisition, Cash Offer Per Share Price All cash offer per share. Offer consideration BusinessAcquisitionCashOfferImpliedValue Business acquisition, all cash offer implied value consideration. Final dividend based on fiscal year end Business Acquisition, Cash Offer Per Share Price, Maximum Final Dividend Based On Fiscal Year End Business Acquisition, Cash Offer Per Share Price, Maximum Final Dividend Based On Fiscal Year End Acquisition conditions, percentage of secured acceptance of voting rights Business Acquisitions, Conditions, Minimum Acceptance Percentage Of Voting Rights Business Acquisitions, Conditions, Minimum Acceptance Percentage Of Voting Rights Unsecured bridge credit agreement maximum borrowing capacity UnsecuredBridgeCreditAgreementMaximumBorrowingCapacity Maximum borrowing capacity, unsecured bridge credit agreement. Unsecured term loan credit agreement maximum borrowing capacity UnsecuredTermLoanCreditAgreementMaximumBorrowingCapacity Maximum borrowing capacity, unsecured term loan agreement. Significant Transactions Significant Transactions [Text Block] The disclosure of significant transactions entered into or completed during the period. Investments Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Statement of Comprehensive Income [Abstract] Net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Unrealized gains (losses) on marketable securities, net of deferred taxes Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax Deferred gains (losses) on cash flow hedges, net of deferred taxes Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax Amounts reclassified to net income: Amounts Reclassified To Net Income [Abstract] Realized (gains) losses on cash flow hedges, net of deferred taxes Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of 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 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 (Loss) Attributable to Noncontrolling Interest Less: Other comprehensive income (loss) attributable to noncontrolling interests Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest Comprehensive income (loss) attributable to Comcast Corporation Comprehensive Income (Loss), Net of Tax, Attributable to Parent Schedule of Fair Value Method Investments [Table] Schedule of Fair Value Method Investments [Table] Schedule of Fair Value Method Investments [Table] Snap [Member] Snap [Member] Snap [Member] 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 securities Payments to Acquire Marketable Securities Contribution from member Member Contribution Contribution from member including, but not limited to, a business, investment or asset. Marketable securities, recognized unrealized gains Equity Securities, FV-NI, Unrealized Gain Equity Securities, FV-NI, Unrealized Gain 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, Gross, Current Less: Allowance for doubtful accounts Allowance for Doubtful Accounts Receivable, Current Receivables, net Noncurrent receivables (included in other noncurrent assets, net) Accounts Receivable, Net, 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 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] Operating 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. Corporate, Non-Segment [Member] Corporate, Non-Segment [Member] Eliminations [Member] Segment Reconciling Items [Member] Theme Parks [Member] Theme Parks [Member] Theme Parks Member NBCUniversal Segments [Member] NBCUniversal Segments [Member] Number of reportable segments Number of Reportable Segments 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. Capital Expenditures Cash Paid for Intangible Assets Total current assets Other intangible assets, net Assets Total current liabilities Deferred income taxes Total equity Total equity Total liabilities and equity Content Licensing And Other [Member] Content Licensing And Other [Member] Content Licensing And Other [Member] Distribution And Other [Member] Distribution And Other [Member] Distribution And Other [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 Revenue Revenue from Contract with Customer [Text Block] Segment Information Segment Reporting Disclosure [Text Block] Earnings Per Share [Abstract] Net Income Attributable to Comcast Corporation Net Income (Loss) Attributable to Parent Basic EPS attributable to Comcast Corporation shareholders (in shares) Weighted Average Number of Shares Outstanding, Basic Basic earnings per common share attributable to Comcast Corporation shareholders (in dollars per share) Earnings Per Share, 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 Diluted earnings per common share attributable to Comcast Corporation shareholders (in dollars per share) Earnings Per Share, Diluted Recent Accounting Pronouncements and Tax Reform New Accounting Pronouncements and Changes in Accounting Principles [Text Block] Computation of diluted EPS Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Operating income Operating Income (Loss) 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] Earnings Per Share Earnings Per Share [Text Block] Schedule of recognized share-based compensation expense Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan [Table Text Block] 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] Cash Payments for Interest and Income Taxes Supplemental Cash Flow Information [Abstract] Interest Interest Paid, Net Income taxes Income Taxes Paid, Net Long-Term Debt Debt Disclosure [Text Block] Commitments and Contingencies Disclosure [Abstract] Temporary Equity, by Class of Stock [Table] Temporary Equity, by Class of Stock [Table] Redeemable Preferred Stock [Member] Redeemable Preferred Stock [Member] Temporary Equity [Line Items] Temporary Equity [Line Items] 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. 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 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 Total costs and expenses Operating income Interest expense Interest Expense Investment and other income (loss), net Income before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Income tax expense Income Tax Expense (Benefit) Net income Net income attributable to Comcast Corporation Basic earnings per common share attributable to Comcast Corporation shareholders (in dollars per share) Diluted earnings per common share attributable to Comcast Corporation shareholders (in dollars per share) Dividends declared per common share (in dollars per share) Common Stock, Dividends, Per Share, Declared Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Senior Notes [Member] Senior 3.90% Notes Due 2038 [Member] Senior 3.90% Notes Due 2038 [Member] Senior 3.90% Notes Due 2038 [Member] Senior 3.55% Notes Due 2028 [Member] Senior 3.55% Notes Due 2028 [Member] Senior 3.55% Notes Due 2028 [Member] Senior 4.00% Notes Due 2048 [Member] Senior 4.00% Notes Due 2048 [Member] Senior 4.00% Notes Due 2048 [Member] Senior 4.25% Notes Due 2053 [Member] Senior 4.25% Notes Due 2053 [Member] Senior 4.25% Notes Due 2053 [Member] Other Borrowings [Member] Other Borrowings [Member] Other Borrowings [Member] Debt face amount Debt Instrument, Face Amount Other Debt Instrument Unamortized Discount Premium Net and Other Borrowings Amount of debt discount (premium) and other borrowings. Interest rate Debt Instrument, Interest Rate, Stated Percentage NBCUniveral Enterprise Senior Floating Rate Notes Due 2018 [Member] NBCUniveral Enterprise Senior Floating Rate Notes Due 2018 [Member] NBCUniveral Enterprise Senior Floating Rate Notes Due 2018 [Member] NBCUniversal Enterprise Senior 1.662% Notes Due 2018 [Member] NBCUniversal Enterprise Senior 1.662% Notes Due 2018 [Member] NBCUniversal Enterprise Senior 1.662% Notes Due 2018 [Member] Senior 5.875% Notes Due 2018 [Member] Senior 5.875% Notes Due 2018 [Member] Senior 5.875% Notes Due 2018 [Member] Other Long-Term Debt [Member] Other Long-Term Debt [Member] Other Long-Term Debt [Member] Repurchases and repayments of debt Capital expenditures incurred but not yet paid Capital Expenditures Incurred but Not yet Paid Dividends payable Dividends Payable Dividends payable (in dollars per share) Dividends Payable, Amount Per Share Assets contributed to variable interest entity Contribution of Property Related Party Transactions Related Party Transactions Disclosure [Text Block] Statement of Cash Flows [Abstract] Operating Activities 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] Share-based compensation Share-based Compensation 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 Deferred Income Tax Expense (Benefit) 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 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. 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] Depreciation Amortization Interest expense Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Total debt Debt and Capital Lease Obligations Fair value of debt Long-term Debt, Fair Value 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 Accumulated Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax Deferred gains (losses) on cash flow hedges Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of 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 Related Party Transactions Condensed Financial Statements Schedule of Related Party Transactions [Table Text Block] Condensed Consolidating Balance Sheet Condensed Balance Sheet [Table Text Block] Condensed Consolidating Statement of Income Condensed Income Statement [Table Text Block] Condensed Consolidating Statement of Cash Flows Condensed Cash Flow Statement [Table Text Block] Comcast and Comcast Cable Debt Securities [Member] Comcast And Comcast Cable Debt Securities [Member] Counterparty Name [Axis] Counterparty Name [Axis] Counterparty Name [Domain] Counterparty Name [Domain] Ownership in cable holding company subsidiaries Ownership In Cable Holding Company Subsidiaries Represents the Company's ownership in its cable holding company subsidiaries. Guarantee obligations, maximum capacity 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 Principal Amount Senior Notes Not Subject To Guarantee Represents the related party aggregate principal amount of senior notes not subject to guarantee by NBCUniversal. Related party credit facility not subject to guarantee Related Party Credit Facility Not Subject To Guarantee Represents the related party credit facility not subject to guarantee by NBCUniversal. 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 by NBCUniversal. Revenue From Contract With Customer Financial Statement Impact Schedule of New Accounting Pronouncements and Changes in Accounting Principles [Table Text Block] Cash and cash equivalents 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 period Debt Borrowings Debt Borrowings [Table Text Block] Debt borrowings table. Debt Repayments and Repurchases Debt Repayments and Repurchases [Table Text Block] Debt Repayments and Repurchases [Text Block] Carrying Value of Related Party Contractual Obligation [Member] Carrying Value Of Related Party Contractual Obligation [Member] Unrealized gains (losses) on marketable securities, deferred taxes Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax Deferred gains (losses) on cash flow hedges, deferred taxes Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax Realized (gains) losses on cash flow hedges, deferred taxes Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax Employee benefit obligations, deferred taxes Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax Currency translation adjustments, deferred taxes Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax Revenue: Revenues [Abstract] Service revenue Sales Revenue, Services, Net Management fee revenue Management Fees Revenue Revenue 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 Accrued expenses and other current liabilities Accrued Expenses And Other Current Liabilities Including Deferred Revenue Accrued Expenses And Other Current Liabilities Including Deferred Revenue Other shareholders’ equity Other stockholders equity Other stockholders equity. Statement of Stockholders' Equity [Abstract] 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] Redeemable Noncontrolling Interest [Member] Redeemable Noncontrolling Interest [Member] Common Stock [Member] Common Stock [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] Noncontrolling Interest [Member] Noncontrolling Interest [Member] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Beginning balance Beginning balance Cumulative effects of adoption of accounting standards Stock compensation plans Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period 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 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 Other Stockholders' Equity, Other Net income (loss) Equity Profit Loss Profit or loss as represented on the statement of changes in equity. Ending balance Ending balance Increase (Decrease) in Temporary Equity [Roll Forward] Increase (Decrease) in Temporary Equity [Roll Forward] Beginning balance 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