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 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 taxes Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax Segment Reporting [Abstract] 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] Accounting Policies [Abstract] 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 2016-13 [Member] Accounting Standards Update 2016-13 [Member] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Retained Earnings [Member] Retained Earnings [Member] New Accounting Pronouncements or Change in Accounting Principle [Line Items] New Accounting Pronouncements or Change in Accounting Principle [Line Items] Cumulative effects of adoption of accounting standards Cumulative Effect of New Accounting Principle in Period of Adoption Organization, Consolidation and Presentation of Financial Statements [Abstract] Condensed Consolidated Financial Statements Business Description and Basis of Presentation [Text Block] Investments [Abstract] Equity in net income (losses) of investees, net Income (Loss) from Equity Method Investments Realized and unrealized gains (losses) on equity securities, net Equity Securities, FV-NI, Gain (Loss) 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) Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Earnings Per Share [Abstract] Earnings Per Share Earnings Per Share [Text Block] Recent Accounting Pronouncements New Accounting Pronouncements and Changes in Accounting Principles [Text Block] Other Industries [Abstract] Owned Film and Television Costs Film Costs [Abstract] Completed, not released: Film Cost Disclosures [Abstract] Remaining nine months of 2020 Film, Monetized On Its Own, Completed And Not Released, Expected Amortization In Remainder Of Fiscal Year Amount of amortization for completed and not released film predominantly monetized on its own and expected to be recognized for the remainder of fiscal year following latest fiscal year Released and programming rights: Film, Monetized On Its Own, Released Film, Expected Amortization [Abstract] Film, Monetized On Its Own, Released Film, Expected Amortization [Abstract] Remaining nine months of 2020 Film, Monetized On Its Own, Released, Expected Amortization, Remainder Of Fiscal Year Amount of amortization for released film predominantly monetized on its own and expected to be recognized in the remainder of fiscal year following latest fiscal year 2021 Film, Monetized On Its Own, Released Film, Expected Amortization, Year Two Amount of amortization for released film predominantly monetized on its own and expected to be recognized within second operating cycle following most recent annual statement of financial position. 2022 Film, Monetized On Its Own, Released Film, Expected Amortization, Year Three Amount of amortization for released film predominantly monetized on its own and expected to be recognized within third operating cycle following most recent annual statement of financial position. Programming Rights Entertainment, License Agreement For Program Material [Abstract] Entertainment, License Agreement For Program Material [Abstract] Released and programming rights: Entertainment, License Agreement For Program Material, Expected Amortization [Abstract] Entertainment, License Agreement For Program Material, Expected Amortization [Abstract] Remaining nine months of 2020 Entertainment, License Agreement For Program Material, Including Sports Rights Advances, Expected Amortization, Remainder Of Fiscal Year Entertainment, license agreement for program material, including sports rights advances, expected amortization to be recognized in the remainder of fiscal year following latest fiscal year 2021 Entertainment, License Agreement For Program Material, Including Sports Rights Advances, Expected Amortization, Year Two Amount of amortization for right acquired by broadcaster under license agreement for program material, including sports rights advances, expected to be recognized within second operating cycle following most recent annual statement of financial position. 2022 Entertainment, License Agreement For Program Material, Including Sports Rights Advances,Expected Amortization, Year Three Amount of amortization for right acquired by broadcaster under license agreement for program material, including sports rights advances, expected to be recognized within third operating cycle following most recent annual statement of financial position. Supplemental Financial Information [Abstract] Statement Of Cash Flows Supplemental Information Abstract Property and equipment and intangible assets accrued 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 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 Owned film and television costs Film, Monetized On Its Own, Amortization Expense Amount of amortization expense for capitalized film cost for film predominantly monetized on its own. Programming rights Entertainment, License Agreement For Program Material, Including Sports Rights Advances, Amortization Expense Amount of amortization expense for rights acquired by broadcaster under license agreement for program material, including sports rights advances. Income Statement [Abstract] Revenue Revenues 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 Costs and Expenses Operating income Operating Income (Loss) 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 (Loss), Including Portion Attributable to Noncontrolling Interest Less: Net income (loss) 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. 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) Debt Disclosure [Abstract] Long-Term Debt Debt Disclosure [Text Block] Business Combinations [Abstract] Schedule of Variable Interest Entities [Table] Schedule of Variable Interest Entities [Table] Ownership [Axis] Ownership [Axis] Ownership [Domain] Ownership [Domain] Universal Beijing Resort [Member] Universal Beijing Resort [Member] Universal Beijing Resort [Member] Consolidated Entities [Axis] Consolidated Entities [Axis] Consolidated Entities [Domain] Consolidated Entities [Domain] Variable Interest Entity, Primary Beneficiary [Member] Variable Interest Entity, Primary Beneficiary [Member] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Universal Beijing Resort Term Loans [Member] Universal Beijing Resort Term Loans [Member] Universal Beijing Resort Term Loans [Member] Variable Interest Entity [Line Items] Variable Interest Entity [Line Items] Ownership percentage in variable interest entity Noncontrolling Interest, Ownership Percentage by Parent Principal amount of term loan outstanding Other Long-term Debt Consolidated variable interest entity's assets included in condensed consolidated balance sheet Assets Consolidated variable interest entity's liabilities included in condensed consolidated balance sheet Liabilities Cover [Abstract] 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] 0.250% Notes Due 2027 [Member] Notes 0.250 percent Due 2027 [Member] Notes 0.250% Due 2027 [Member] 1.500% Notes Due 2029 [Member] Notes 1.500 percent Due 2029 [Member] Notes 1.500% Due 2029 [Member] 0.750% Notes Due 2032 [Member] Notes 0.750 percent due 2032 [Member] Notes 0.750% due 2032 [Member] 1.875% Notes Due 2036 [Member] Notes 1.875 percent due 2036 [Member] Notes 1.875% due 2036 [Member] 1.250% Notes Due 2040 [Member] Notes 1.250 percent due 2040 [Member] Notes 1.250% due 2040 [Member] 9.455% Guaranteed Notes Due 2022 [Member] Guaranteed Notes 9.455 Percent Due 2022 [Member] Guaranteed Notes 9.455% Due 2022 [Member] 5.50% Notes Due 2029 [Member] Notes 5.50 Percent Due 2029 [Member] Notes 5.50% Due 2029 [Member] 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] 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] Document Type Document Type Document Fiscal Period Focus Document Fiscal Period Focus Document Quarterly Report Document Quarterly 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 File Number Entity File Number Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key 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 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 Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Segment Information Segment Reporting Disclosure [Text Block] Programming and Production Costs Entertainment [Text Block] Revenues [Abstract] Revenue Revenue from Contract with Customer [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. Investment Summary Summary Investment Holdings [Table Text Block] Intangible Assets, Net (Excluding Goodwill) [Abstract] Remaining nine months of 2020 Finite-Lived Intangible Assets, Amortization Expense, Remainder of Fiscal Year 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 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] Share-based Payment Arrangement, Noncash Expense [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] Award Type [Domain] Award Type [Domain] Restricted share units [Member] Restricted Stock Units (RSUs) [Member] Stock options [Member] Share-based Payment Arrangement, 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 Share-based Payment Arrangement, Expense Unrecognized pretax compensation expense on nonvested awards Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount Computation of diluted EPS Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Significant Transactions Significant Transactions [Text Block] The disclosure of significant transactions entered into or completed during the period. Schedule of Indefinite-Lived Intangible Assets [Table] Schedule of Indefinite-Lived Intangible Assets [Table] 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] Franchise Rights [Member] Franchise Rights [Member] Trade Names [Member] Trade Names [Member] FCC Licenses [Member] Operating and Broadcast Rights [Member] Indefinite-lived Intangible Assets [Line Items] Indefinite-lived Intangible Assets [Line Items] Gross Carrying Amount Indefinite-lived Intangible Assets (Excluding Goodwill) Schedule of Finite-Lived Intangible Assets [Table] Schedule of Finite-Lived Intangible Assets [Table] 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] Software [Member] Computer Software, Intangible Asset [Member] Other Agreements and Rights [Member] Other Intangible Assets [Member] Finite-Lived Intangible Assets [Line Items] Finite-Lived Intangible Assets [Line Items] Weighted-Average Original Useful Life Finite-Lived Intangible Asset, Useful Life Gross Carrying Amount Finite-Lived Intangible Assets, Gross Accumulated Amortization Finite-Lived Intangible Assets, Accumulated Amortization Total Intangible Assets, Gross (Excluding Goodwill) Summary of Intangible Assets Schedule Of Finite-Lived And Indefinite-Lived Intangible Assets [Table Text Block] Schedule Of Finite-Lived And Indefinite-Lived Intangible Assets [Table Text Block] Amortization of Intangible Assets Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block] Statement of Cash Flows [Abstract] Operating Activities Net Cash Provided by (Used in) Operating Activities [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 and amortization Depreciation, Depletion and Amortization 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 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 Net Cash Provided by (Used in) Operating Activities Investing Activities Net Cash Provided by (Used in) Investing Activities [Abstract] Capital expenditures Payments to Acquire Property, Plant, and Equipment Cash paid for intangible assets Payments to Acquire Intangible Assets 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 Repurchases and repayments of debt Repayments of Other Debt Repurchases of common stock under 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 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, 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 Intangible Assets Intangible Assets Disclosure [Text Block] Investments Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Disaggregation of Revenue [Table] Disaggregation of Revenue [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] Eliminations [Member] Segment Reconciling Items [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 NBCUniversal Segments [Member] NBCUniversal Segments [Member] Sky Limited [Member] Sky Limited [Member] Sky Limited [Member] Product and Service [Axis] Product and Service [Axis] Product and Service [Domain] Product and Service [Domain] 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] Business Services [Member] Business Services [Member] Business Services [Member] Direct To Consumer [Member] Direct To Consumer [Member] Direct To Consumer [Member] Distribution [Member] Distribution [Member] Distribution Content [Member] Content [Member] Content [Member] Advertising [Member] Advertising [Member] Theatrical [Member] Theatrical [Member] Theatrical [Member] Content Licensing And Other [Member] Content Licensing And Other [Member] Content Licensing And Other [Member] Content Licensing [Member] Content Licensing [Member] Content Licensing [Member] Distribution And Other [Member] Distribution And Other [Member] Distribution And Other [Member] Home Entertainment [Member] Home Entertainment [Member] Home Entertainment [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] Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] 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 Receivables, gross Accounts Receivable, before Allowance for Credit Loss, Current Less: Allowance for doubtful accounts Accounts Receivable, Allowance for Credit Loss, Current Receivables, net Accounts Receivable, after Allowance for Credit Loss, Current Noncurrent receivables, net (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 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 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: 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 Commitments And Contingencies [Table] Commitment And Contingencies [Table] Commitment And Contingencies [Table] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] NBCUniversal Enterprise [Member] NBCUniversal Enterprise [Member] Redeemable Subsidiary Preferred Stock [Member] Redeemable Preferred Stock [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] Commitments And Contingencies [Line Items] Commitment And Contingencies [Line Items] [Line Items] for Commitment And Contingencies [Table] 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”). 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. 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 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. Counterparty Name [Axis] Counterparty Name [Axis] Counterparty Name [Domain] Counterparty Name [Domain] Schedule of Equity Method Investments [Line Items] Schedule of Equity Method Investments [Line Items] 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 investment Equity Method Investments Recognition of previously deferred gain Deferred Gain Recognized On Dilution Of Equity Method Investment Deferred Gain Recognized On Dilution Of Equity Method Investment Cash capital contributions for equity method investments Payments to Acquire Equity Method 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. 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. Collateralized obligation Collateralized Obligation Carrying amount of obligation presented separately as collateralized obligation that is secured by assets. Fair value of collateralized obligation Collateralized Obligation, Fair Value Fair value of obligation presented separately as collateralized obligation that is secured by assets. 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 Programming rights Entertainment, License Agreement For Program Material, Including Sports Rights Advances, Capitalized Cost, Current Amount of capitalized cost for rights acquired by broadcaster under license agreement for program material, including sports rights advances, 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, Monetized On Its Own, And Entertainment, License Agreement For Program Material, Including Sports Rights Advances, Capitalized Costs, Noncurrent Amount of capitalized film cost for film predominantly monetized on its own and capitalized cost for rights acquired by broadcaster under license agreement for program material, including sports rights advances, noncurrent. 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 of accumulated depreciation of $53,566 and $53,239 Property, Plant and Equipment, Net Goodwill Goodwill Franchise rights Indefinite-Lived Franchise Rights Other intangible assets, net of accumulated amortization of $16,292 and $17,217 Other Intangible Assets, Net Other noncurrent assets, net Other Assets, Noncurrent Total 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. Deferred revenue Deferred Revenue, Current Accrued expenses and other current liabilities Accrued Liabilities, Current 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 Deferred income taxes Deferred Income Tax Liabilities, Net Other noncurrent liabilities Other Liabilities, Noncurrent Commitments and contingencies (Note 12) 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 Accumulated other comprehensive income (loss) Total Comcast Corporation shareholders’ equity Stockholders' Equity Attributable to Parent Noncontrolling interests Stockholders' Equity Attributable to Noncontrolling Interest Total equity Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Total liabilities and equity Liabilities and Equity Schedule of Fair Value Method Investments [Table] Schedule of Fair Value Method Investments [Table] Schedule of Fair Value Method Investments [Table] Peloton [Member] Peloton [Member] Peloton 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] Marketable equity securities Equity Securities, FV-NI Marketable equity securities, recognized unrealized gains (losses) Equity Securities, FV-NI, Unrealized Gain (Loss) 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] Common Stock [Member] Common Stock [Member] Additional Paid-in Capital [Member] Additional Paid-in Capital [Member] Treasury Stock at Cost [Member] Treasury Stock [Member] Accumulated Other Comprehensive Income (Loss) [Member] AOCI Attributable to Parent [Member] Noncontrolling Interest [Member] Noncontrolling Interest [Member] 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 Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Beginning balance Stock compensation plans APIC, Share-based Payment Arrangement, Increase for Cost Recognition Repurchases of common stock under 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) Net income (loss) Net Income (Loss) Attributable to Noncontrolling Interest Ending balance Cash dividends declared per common share (in dollars per share) Common Stock, Dividends, Per Share, Declared 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 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] 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 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] 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. Depreciation and Amortization Depreciation, Depletion and Amortization, Nonproduction Capital Expenditures Cash Paid for Intangible Assets Property and equipment - accumulated depreciation Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Other 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 Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Sky Senior Notes Due 2020 [Member] Sky Senior Notes Due 2020 [Member] Sky Senior Notes Due 2020 [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] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent Event [Member] Subsequent Event [Member] Debt Instrument [Line Items] Debt Instrument [Line Items] Total carrying value of debt Debt and Lease Obligation Total fair value of debt Long-term Debt, Fair Value Repayments of senior notes Basis of Presentation Basis of Accounting, Policy [Policy Text Block] Film and Television Costs Film Costs, Policy [Policy Text Block] Entertainment Entities Entertainment Entities, Policy [Policy Text Block] Film Costs and Entertainment Entities Film Costs And Entertainment Entities, Policy [Policy Text Block] Disclosure of accounting policy for film costs related to film libraries and for entertainment entities. Earnings Per Share Earnings Per Share, Policy [Policy Text Block] Recent Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Equity method Nonmarketable equity securities Equity Securities without Readily Determinable Fair Value, Amount Other investments Other Investments Total investments Investments Less: Current investments Short-term Investments Less: Investment securing collateralized obligation Noncurrent investments Film and Television Costs Released, less amortization Film, Monetized On Its Own, Capitalized Cost, Released Amount of capitalized film cost for released film predominantly monetized on its own. Completed, not released Film, Monetized On Its Own, Capitalized Cost, Completed And Not Released Amount of capitalized film cost for completed and not released film predominantly monetized on its own. In production and in development Film, Monetized On Its Own, Capitalized Cost, In Production And In Development Amounts of capitalized film cost incurred in production and in development of film predominantly monetized on its own Film and Television Costs Film, Monetized On Its Own, Capitalized Cost Film, Monetized On Its Own, Capitalized Cost Programming rights, less amortization Entertainment, License Agreement For Program Material, Including Sports Rights Advances, Capitalized Cost Amount of capitalized cost for rights acquired by broadcaster under license agreement for program material, including sports rights advances. Total film and television costs and programming rights Film, Monetized On Its Own Capitalized Cost, And Entertainment, License Agreement For Program Material, Including Sports Rights Advances Total amounts of capitalized film cost for film predominantly monetized on its own and capitalized cost for rights acquired by broadcaster under license agreement for program material, including sports rights advances. Less: Current portion of programming rights Film and television costs 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. Film Costs Theatrical Film Costs Television Costs Direct-to-television Film Costs [Abstract] Released, less amortization Direct-to-television Film Costs, Released Completed, not released Direct-to-television Film Costs, Completed and Not 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. Television Costs Direct-to-television Film Costs Total Film Costs Under Previous Guidance [Abstract] Film Costs Under Previous Guidance [Abstract] [Abstract] Released, less amortization Theatrical Film Costs And Direct-To-Television Costs, Released Theatrical Film Costs And Direct-To-Television Costs, Released Completed, not released Theatrical Film Costs And Direct-To-Television Costs, Completed And Not Released Theatrical Film Costs And Direct-To-Television Costs, Completed And Not Released In production and in development Theatrical Film Costs And Direct-to-Television Costs, In Production And In Development Theatrical Film Costs And Direct-to-Television Costs, In Production And In Development Total Film Costs Programming rights, less amortization Programming Rights Less Amortization The carrying amount of total acquired programming rights, less amortization Total film and 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 Film and television costs 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 Interest expense Schedule of recognized share-based compensation expense Share-based Payment Arrangement, Cost 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] Investment Holdings [Table] Investment Holdings [Table] AirTouch [Member] Air Touch [Member] Air Touch [member] Air Touch [Member] Schedule of Other Investments [Line Items] Schedule of Held-to-maturity Securities [Line Items] Number of series of preferred stock Number of Preferred Stock Series Number of Preferred Stock Series Held to maturity investment Debt Securities, Held-to-maturity, Current Redeemable subsidiary preferred shares Carrying Amount Of Redeemable Preferred Stock Carrying amount of redeemable preferred stock Cash payments received upon redemption of preferred stock Proceeds from Maturities, Prepayments and Calls of Held-to-maturity Securities Cash payments for the redemption of redeemable preferred shares Payments For Repurchase and Redemption of Subsidiary Preferred Stock The cash outflow for repurchase and redemption of subsidiary preferred stock. Supplemental Financial Information Additional Financial Information Disclosure [Text Block] Amortization of Film and Television Costs Amortization Of Film And TV Costs [Table Text Block] Total amount of amortization expense for both capitalized cost of owned film and television costs and for rights acquired by broadcaster under license agreement for program material, including sports rights advances, recorded in programming and production costs Capitalized Film and Television Costs and Programming Rights Schedule Of Capitalized Film And Television Costs [Table Text Block] Schedule of capitalized costs for film predominantly monetized on its own and for rights acquired by broadcaster under license agreement for program material, including sports rights advances, recorded at the balance sheet date. Estimated Future Amortization Expense for Capitalized Film and Television Costs and Programming Rights Schedule Of Estimated Future Amortization Expense For Capitalized Film And Television Cost [Table Text Block] Schedule of estimated future amortization of capitalized costs for film predominantly monetized on its own and for rights acquired by broadcaster under license agreement for program material, including sports rights advances, recorded at the balance sheet date.