v2.4.1.9

Related Party Transactions - Consolidated Statement of Income (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Revenue	$ 17,853,000,000us-gaap_Revenues	$ 17,408,000,000us-gaap_Revenues
NBCUniversal Media, LLC [Member]
Revenue	6,604,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	6,876,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Transactions With Comcast And Consolidated Subsidiaries [Member] | NBCUniversal Media, LLC [Member]
Revenue	342,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = cmcsa_ComcastAndConsolidatedSubsidiariesMember	361,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = cmcsa_ComcastAndConsolidatedSubsidiariesMember
Operating costs and expenses	(50,000,000)cmcsa_OperatingExpensesExcludingDepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = cmcsa_ComcastAndConsolidatedSubsidiariesMember	(37,000,000)cmcsa_OperatingExpensesExcludingDepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = cmcsa_ComcastAndConsolidatedSubsidiariesMember
Other income (expense)	$ (9,000,000)cmcsa_OtherIncomeExpenseRelatedParty / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = cmcsa_ComcastAndConsolidatedSubsidiariesMember	$ (9,000,000)cmcsa_OtherIncomeExpenseRelatedParty / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = cmcsa_ComcastAndConsolidatedSubsidiariesMember

X

- Definition

Operating costs and expenses including amortization of film and television costs but excluding intangible amortization and depreciation.

+ References

No definition available.

+ Details

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Namespace Prefix:	cmcsa_
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Balance Type:	debit
Period Type:	duration

X

- Definition

Represents all of the intercompany transactions with Comcast Corporation which are included in other income (expense) captions.

+ References

No definition available.

+ Details

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Namespace Prefix:	cmcsa_
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Balance Type:	credit
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X

- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Article 5

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- Details

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X

- Details

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Data Type:	na
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