v2.4.1.9

Supplemental Financial Information (Cash Payments for Interest and Income Taxes)(Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Interest | $ 2,389 us-gaap_InterestPaidNet | $ 2,355 us-gaap_InterestPaidNet | $ 2,314 us-gaap_InterestPaidNet
Income taxes | 3,668 us-gaap_IncomeTaxesPaidNet | 3,946 us-gaap_IncomeTaxesPaidNet | 2,841 us-gaap_IncomeTaxesPaidNet
NBCUniversal Media, LLC [Member] |  |  |
Interest | 485 us-gaap_InterestPaidNet / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | 462 us-gaap_InterestPaidNet / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | 461 us-gaap_InterestPaidNet / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Income taxes | $ 174 us-gaap_IncomeTaxesPaidNet / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | $ 205 us-gaap_IncomeTaxesPaidNet / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | $ 169 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

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: |