Related Party Transactions (Condensed Consolidated Statement of Income) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Related Party Transaction [Line Items]
Revenue	$ 21,165	$ 19,269	$ 41,628	$ 38,059
Operating costs and expenses	659	708	1,284	1,262
NBCUniversal Media LLC [Member]
Related Party Transaction [Line Items]
Revenue	8,331	7,103	16,199	13,964
Operating costs and expenses	164	175	308	203
Comcast And Consolidated Subsidiaries [Member] \| NBCUniversal Media LLC [Member]
Related Party Transaction [Line Items]
Revenue	460	406	919	813
Operating costs and expenses	(49)	(44)	(110)	(104)
Other income (expense)	$ (28)	$ (17)	$ (47)	$ (30)

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

No definition available.

+ Details

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

- Definition

The aggregate amount of income or expense from ancillary business-related activities (that is to say, excluding major activities considered part of the normal operations of the business).

+ 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 210.5-03.7)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

+ Details

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- 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

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Namespace Prefix:	us-gaap_
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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=63488584&loc=d3e20235-122688

+ Details

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Balance Type:	credit
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- Details

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Namespace Prefix:
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- Details

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