v2.4.1.9

Supplemental Financial Information (Cash Payments for Interest and Income Taxes)(Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Interest	$ 691us-gaap_InterestPaidNet	$ 623us-gaap_InterestPaidNet
Income taxes	118us-gaap_IncomeTaxesPaidNet	186us-gaap_IncomeTaxesPaidNet
NBCUniversal Media, LLC [Member]
Interest	33us-gaap_InterestPaidNet / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	36us-gaap_InterestPaidNet / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Income taxes	$ 40us-gaap_IncomeTaxesPaidNet / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	$ 53us-gaap_IncomeTaxesPaidNet / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember

X

- Definition

The amount of cash paid during the current period to foreign, federal, state, and local authorities as taxes on income, net of any cash received during the current period as refunds for the overpayment of taxes.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4297-108586

+ Details

Name:	us-gaap_IncomeTaxesPaidNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

The amount of cash paid for interest during the period net of cash paid for interest that is capitalized.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4297-108586

+ Details

Name:	us-gaap_InterestPaidNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Details

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