v2.4.1.9

Related Party Transactions (Narrative) (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Other noncurrent liabilities	$ 10,837,000,000us-gaap_OtherLiabilitiesNoncurrent	$ 10,819,000,000us-gaap_OtherLiabilitiesNoncurrent
NBCUniversal Media, LLC [Member]
Borrowing margin for LIBOR based borrowings	1.00%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1 / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Other noncurrent liabilities	3,692,000,000us-gaap_OtherLiabilitiesNoncurrent / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	3,722,000,000us-gaap_OtherLiabilitiesNoncurrent / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Nbcuniversal Holdings Preferred Stock [Member] | NBCUniversal Media, LLC [Member]
Preferred stock liquidation preference value	9,400,000,000us-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	383,000,000us-gaap_OtherLiabilitiesNoncurrent / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = cmcsa_CarryingValueOfRelatedPartyContractualObligationMember
Comcast Corporation And NBCUniversal Media LLC Revolving Credit Agreement [Member] | NBCUniversal Media, LLC [Member]
Revolving Credit Agreement Capacity	$ 3,000,000,000cmcsa_RevolvingCreditAgreementCapacity / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = cmcsa_ComcastCorporationAndNBCUniversalMediaLLCRevolvingCreditAgreementMember

X

- 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

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Namespace Prefix:	cmcsa_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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
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X

- 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

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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X

- 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
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X

- Definition

Value of the difference between preference in liquidation and the par or stated values of the preferred shares.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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X

- Details

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Namespace Prefix:
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- Details

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X

- Details

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Namespace Prefix:
Data Type:	na
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X

- Details

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