v3.7.0.1

Related Party Transactions (Condensed Consolidated Statement of Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Related Party Transaction [Line Items]
Revenue	$ 20,463	$ 18,790
NBCUniversal Media LLC [Member]
Related Party Transaction [Line Items]
Revenue	7,868	6,861
Comcast And Consolidated Subsidiaries [Member] | NBCUniversal Media LLC [Member]
Related Party Transaction [Line Items]
Revenue	459	406
Operating costs and expenses	(61)	(60)
Other income (expense)	$ (19)	$ (13)

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_
Data Type:	xbrli:monetaryItemType
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

Name:	cmcsa_OtherIncomeExpenseRelatedParty
Namespace Prefix:	cmcsa_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_RelatedPartyTransactionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

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=63488584&loc=d3e20235-122688

+ Details

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X

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=cmcsa_ComcastAndConsolidatedSubsidiariesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: