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Significant Transactions (Narrative) (Details) (USD $)
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12 Months Ended |
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Dec. 31, 2013
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Dec. 31, 2014
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Mar. 19, 2013
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| Significant Transactions [Line Items] |
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| Purchase of NBCUniversal noncontrolling interest |
$ 16,700,000,000cmcsa_ConsiderationTransferredToAcquireAdditionalInterestInSubsidiaries |
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| Consideration transferred related to the Redemption Transaction and purchase of certain properties |
725,000,000cmcsa_ConsiderationTransferredRelatedToRedemptionTransactionByFundingSource |
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| Remaining equity interest acquired |
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49.00%cmcsa_NoncontrollingInterestAcquired |
| Company Shares Exchanged For Each Acquiree Share |
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2.875cmcsa_CompanySharesExchangedForEachAcquireeShare |
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| NBCUniversal Media, LLC [Member] |
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| Significant Transactions [Line Items] |
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| Purchase of NBCUniversal noncontrolling interest |
16,700,000,000cmcsa_ConsiderationTransferredToAcquireAdditionalInterestInSubsidiaries / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember |
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| Consideration transferred related to the Redemption Transaction and purchase of certain properties |
725,000,000cmcsa_ConsiderationTransferredRelatedToRedemptionTransactionByFundingSource / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember |
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| Remaining equity interest acquired |
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49.00%cmcsa_NoncontrollingInterestAcquired / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember |
| Redemption percentage |
15.00%cmcsa_RedemptionPercentage / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember |
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| Comcast Corporation [Member] | NBCUniversal Media, LLC [Member] |
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| Significant Transactions [Line Items] |
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| Ownership percentage in NBCUniversal Holdings |
96.00%cmcsa_OwnershipPercentage / us-gaap_BusinessAcquisitionAxis = cmcsa_ComcastCorporationMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember |
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| Comcast Cash On Hand |
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| Significant Transactions [Line Items] |
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| Consideration transferred related to the Redemption Transaction and purchase of certain properties |
11,400,000,000cmcsa_ConsiderationTransferredRelatedToRedemptionTransactionByFundingSource / us-gaap_BusinessAcquisitionAxis = us-gaap_CashMember |
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| Comcast Cash On Hand | NBCUniversal Media, LLC [Member] |
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| Significant Transactions [Line Items] |
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| Consideration transferred related to the Redemption Transaction and purchase of certain properties |
11,400,000,000cmcsa_ConsiderationTransferredRelatedToRedemptionTransactionByFundingSource / us-gaap_BusinessAcquisitionAxis = us-gaap_CashMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember |
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| NBCUniversal Cash On Hand [Member] | NBCUniversal Media, LLC [Member] |
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| Significant Transactions [Line Items] |
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| Portion Of Consideration Transferred Funded By NBCUniversal |
4,600,000,000cmcsa_PortionOfConsiderationTransferredFundedByNbcuniversal / us-gaap_BusinessAcquisitionAxis = cmcsa_NbcuniversalCashOnHandMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember |
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| NBCUniversal Enterprise Senior Unsecured Debt Securities [Member] |
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| Significant Transactions [Line Items] |
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| Consideration transferred related to the Redemption Transaction and purchase of certain properties |
4,000,000,000cmcsa_ConsiderationTransferredRelatedToRedemptionTransactionByFundingSource / us-gaap_BusinessAcquisitionAxis = us-gaap_SeniorNotesMember |
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| NBCUniversal Enterprise Senior Unsecured Debt Securities [Member] | NBCUniversal Media, LLC [Member] |
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| Significant Transactions [Line Items] |
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| Consideration transferred related to the Redemption Transaction and purchase of certain properties |
4,000,000,000cmcsa_ConsiderationTransferredRelatedToRedemptionTransactionByFundingSource / us-gaap_BusinessAcquisitionAxis = us-gaap_SeniorNotesMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember |
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| Commercial Paper Program |
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| Significant Transactions [Line Items] |
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| Consideration transferred related to the Redemption Transaction and purchase of certain properties |
750,000,000cmcsa_ConsiderationTransferredRelatedToRedemptionTransactionByFundingSource / us-gaap_BusinessAcquisitionAxis = us-gaap_CommercialPaperMember |
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| Commercial Paper Program | NBCUniversal Media, LLC [Member] |
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| Significant Transactions [Line Items] |
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| Consideration transferred related to the Redemption Transaction and purchase of certain properties |
750,000,000cmcsa_ConsiderationTransferredRelatedToRedemptionTransactionByFundingSource / us-gaap_BusinessAcquisitionAxis = us-gaap_CommercialPaperMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember |
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| Nbcuniversal Holdings Preferred Stock [Member] | NBCUniversal Media, LLC [Member] |
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| Significant Transactions [Line Items] |
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| Preferred stock dividend rate percentage |
8.25%us-gaap_PreferredStockDividendRatePercentage / us-gaap_BusinessAcquisitionAxis = cmcsa_NbcuniversalHoldingsPreferredStockMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember |
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| Preferred stock liquidition preference value |
9,400,000,000us-gaap_PreferredStockLiquidationPreferenceValue / us-gaap_BusinessAcquisitionAxis = cmcsa_NbcuniversalHoldingsPreferredStockMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember |
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| Preferred stock dividend reset rate percentage description |
On March 1, 2018, and thereafter on every fifth anniversary of such date, this rate will reset to 7.44% plus the yield on actively traded United States Treasury securities having a 5 year maturity. |
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| Thirty Rockefeller Plaza And Englewood Cliffs [Member] |
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| Significant Transactions [Line Items] |
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| Payments related to acquisition of real estate properties |
1,400,000,000cmcsa_PaymentsRelatedToAcquisitionOfBuildings / us-gaap_BusinessAcquisitionAxis = cmcsa_ThirtyRockefellerPlazaAndEnglewoodCliffsMember |
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| Thirty Rockefeller Plaza And Englewood Cliffs [Member] | NBCUniversal Media, LLC [Member] |
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| Significant Transactions [Line Items] |
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| Payments related to acquisition of real estate properties |
1,400,000,000cmcsa_PaymentsRelatedToAcquisitionOfBuildings / us-gaap_BusinessAcquisitionAxis = cmcsa_ThirtyRockefellerPlazaAndEnglewoodCliffsMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember |
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| NBCUniversal Enterprise [Member] |
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| Significant Transactions [Line Items] |
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| Preferred stock dividend rate percentage |
5.25%us-gaap_PreferredStockDividendRatePercentage / us-gaap_BusinessAcquisitionAxis = cmcsa_NbcuniversalEnterpriseMember |
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| Fair value of redeemable preferred stock |
741,000,000cmcsa_FairValueAmountOfRedeemablePreferredStock / us-gaap_BusinessAcquisitionAxis = cmcsa_NbcuniversalEnterpriseMember |
751,000,000cmcsa_FairValueAmountOfRedeemablePreferredStock / us-gaap_BusinessAcquisitionAxis = cmcsa_NbcuniversalEnterpriseMember |
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| NBCUniversal Enterprise [Member] | NBCUniversal Media, LLC [Member] |
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| Significant Transactions [Line Items] |
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| Ownership percentage in NBCUniversal Holdings |
4.00%cmcsa_OwnershipPercentage / us-gaap_BusinessAcquisitionAxis = cmcsa_NbcuniversalEnterpriseMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember |
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| Merger Agreement Undertaking Number Of Divested Customers [Member] |
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| Significant Transactions [Line Items] |
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| Number of customers |
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3,000,000cmcsa_NumberOfCustomers / us-gaap_BusinessAcquisitionAxis = cmcsa_MergerAgreementUndertakingNumberOfDivestedCustomersMember |
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| Comcast Corporate Shareholders [Member] |
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| Significant Transactions [Line Items] |
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| Ownership Percentage In SpinCo |
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67.00%cmcsa_OwnershipPercentageInSpinco / us-gaap_BusinessAcquisitionAxis = cmcsa_ComcastCorporateShareholdersMember |
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| New Charter [Member] |
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| Significant Transactions [Line Items] |
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| Ownership Percentage In SpinCo |
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33.00%cmcsa_OwnershipPercentageInSpinco / us-gaap_BusinessAcquisitionAxis = cmcsa_NewCharterMember |
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| Transaction-Related Expenses [Member] |
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| Significant Transactions [Line Items] |
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| Other operating and administrative expenses |
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237,000,000cmcsa_Transactioncostsandtransactionrelatedcostsinoperatingcostsandexpenses / us-gaap_BusinessAcquisitionAxis = cmcsa_TransactionRelatedExpensesMember |
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| NBCUniversal Enterprise Credit Facility [Member] |
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| Significant Transactions [Line Items] |
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| Consideration transferred related to the Redemption Transaction and purchase of certain properties |
1,250,000,000cmcsa_ConsiderationTransferredRelatedToRedemptionTransactionByFundingSource / us-gaap_BusinessAcquisitionAxis = cmcsa_NbcuniversalEnterpriseCreditFacilityMember |
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| NBCUniversal Enterprise Credit Facility [Member] | NBCUniversal Media, LLC [Member] |
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| Significant Transactions [Line Items] |
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| Consideration transferred related to the Redemption Transaction and purchase of certain properties |
$ 1,250,000,000cmcsa_ConsiderationTransferredRelatedToRedemptionTransactionByFundingSource / us-gaap_BusinessAcquisitionAxis = cmcsa_NbcuniversalEnterpriseCreditFacilityMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember |
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