v2.4.1.9

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

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- 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

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