v2.4.1.9

Related Party Transactions - Consolidated Statement of Income (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenue	$ 17,732,000,000us-gaap_Revenues	$ 16,791,000,000us-gaap_Revenues	$ 16,844,000,000us-gaap_Revenues	$ 17,408,000,000us-gaap_Revenues	$ 16,926,000,000us-gaap_Revenues	$ 16,151,000,000us-gaap_Revenues	$ 16,270,000,000us-gaap_Revenues	$ 15,310,000,000us-gaap_Revenues	$ 68,775,000,000us-gaap_Revenues	$ 64,657,000,000us-gaap_Revenues	$ 62,570,000,000us-gaap_Revenues
NBCUniversal Media, LLC [Member]
Revenue									25,428,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	23,650,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	23,812,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Transactions With Comcast And Consolidated Subsidiaries [Member] | NBCUniversal Media, LLC [Member]
Revenue									1,315,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = cmcsa_ComcastAndConsolidatedSubsidiariesMember	1,262,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = cmcsa_ComcastAndConsolidatedSubsidiariesMember	1,228,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = cmcsa_ComcastAndConsolidatedSubsidiariesMember
Operating costs and expenses									(162,000,000)cmcsa_OperatingExpensesExcludingDepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = cmcsa_ComcastAndConsolidatedSubsidiariesMember	(190,000,000)cmcsa_OperatingExpensesExcludingDepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = cmcsa_ComcastAndConsolidatedSubsidiariesMember	(175,000,000)cmcsa_OperatingExpensesExcludingDepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = cmcsa_ComcastAndConsolidatedSubsidiariesMember
Other income (expense)									$ (43,000,000)cmcsa_OtherIncomeExpenseRelatedParty / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = cmcsa_ComcastAndConsolidatedSubsidiariesMember	$ 0cmcsa_OtherIncomeExpenseRelatedParty / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = cmcsa_ComcastAndConsolidatedSubsidiariesMember	$ 0cmcsa_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.

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X

- Definition

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+ References

No definition available.

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- 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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