v2.4.1.9

Related Party Transactions (Narrative) (Details) (USD $) | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Borrowing margin for LIBOR based borrowings | 1.00%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1 |  |
Settlement Of Station Venture Liability | $ 0 cmcsa_SettlementOfStationVentureLiability | $ 602,000,000 cmcsa_SettlementOfStationVentureLiability | $ 0 cmcsa_SettlementOfStationVentureLiability
Other noncurrent liabilities | 10,819,000,000 us-gaap_OtherLiabilitiesNoncurrent | 11,384,000,000 us-gaap_OtherLiabilitiesNoncurrent |
NBCUniversal Media, LLC [Member] |  |  |
Revolving Credit Agreement Capacity |  | 3,000,000,000 cmcsa_RevolvingCreditAgreementCapacity / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember |
Collateral Liability For Unconsolidated Subsidiary Debt |  | 482,000,000 cmcsa_CollateralLiabilityForUnconsolidatedSubsidiaryDebt / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember |
Borrowing margin for LIBOR based borrowings | 1.00%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1 / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember |  |
Settlement Of Station Venture Liability | 0 cmcsa_SettlementOfStationVentureLiability / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | 602,000,000 cmcsa_SettlementOfStationVentureLiability / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | 0 cmcsa_SettlementOfStationVentureLiability / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Redemption transaction distribution | 0 cmcsa_RedemptionTransactionDistribution / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | 3,200,000,000 cmcsa_RedemptionTransactionDistribution / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | 0 cmcsa_RedemptionTransactionDistribution / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Other noncurrent liabilities | 3,722,000,000 us-gaap_OtherLiabilitiesNoncurrent / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | 3,412,000,000 us-gaap_OtherLiabilitiesNoncurrent / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember |
Nbcuniversal Holdings Preferred Stock [Member] | NBCUniversal Media, LLC [Member] |  |  |
Preferred stock liquidition preference value | 9,400,000,000 us-gaap_PreferredStockLiquidationPreferenceValue / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = cmcsa_NbcuniversalHoldingsPreferredStockMember |  |
Preferred stock dividend rate percentage | 8.25%us-gaap_PreferredStockDividendRatePercentage / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = cmcsa_NbcuniversalHoldingsPreferredStockMember |  |
Carrying Value Of Related Party Contractual Obligation [Member] | NBCUniversal Media, LLC [Member] |  |  |
Other noncurrent liabilities | $ 383,000,000 us-gaap_OtherLiabilitiesNoncurrent / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = cmcsa_CarryingValueOfRelatedPartyContractualObligationMember | $ 383,000,000 us-gaap_OtherLiabilitiesNoncurrent / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = cmcsa_CarryingValueOfRelatedPartyContractualObligationMember |

X
- Definition Collateral Liability For Unconsolidated Subsidiary Debt + References No definition available. + Details
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Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition The cash distribution to NBCUniversal Holdings associated with the redemption transaction. + References No definition available. + Details
Name: | cmcsa_RedemptionTransactionDistribution
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition The maximum amount of borrowing or lending capacity with respect to the cash management arrangement between Comcast and NBCUniversal under the revolving credit agreement. + References No definition available. + Details
Name: | cmcsa_RevolvingCreditAgreementCapacity
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition The cash outflow associated with the settlement of the Station Venture liability. + References No definition available. + Details
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Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Percentage points added to the reference rate to compute the variable rate on the debt instrument. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Aggregate carrying amount, as of the balance sheet date, of noncurrent obligations not separately disclosed in the balance sheet. Noncurrent liabilities are expected to be paid after one year (or the normal operating cycle, if longer). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.24) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 24 -Article 5 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition The percentage rate used to calculate dividend payments on preferred stock. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Value of the difference between preference in liquidation and the par or stated values of the preferred shares. + References No definition available. + Details
Name: | us-gaap_PreferredStockLiquidationPreferenceValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |