v3.7.0.1

Related Party Transactions (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
Other noncurrent liabilities	$ 10,677	$ 10,925
NBCUniversal Media LLC [Member]
Related Party Transaction [Line Items]
Other noncurrent liabilities	4,039	$ 4,130
NBCUniversal Media LLC [Member] | Carrying Value Of Related Party Contractual Obligation [Member]
Related Party Transaction [Line Items]
Other noncurrent liabilities	$ 383

X

- Definition

Amount of liabilities classified as other, due 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

+ Details

Name:	us-gaap_OtherLiabilitiesNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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

- Details

Name:	dei_LegalEntityAxis=cmcsa_NBCUniversalMediaLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

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