v2.4.1.9

Goodwill and Other Intangible Assets (Amortization of Intangible Assets) (Details) (USD $) In Millions, unless otherwise specified | Dec. 31, 2014
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Future amortization expense, 2015 | $ 1,619 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths
Future amortization expense, 2016 | 1,457 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo
Future amortization expense, 2017 | 1,296 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree
Future amortization expense, 2018 | 1,053 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour
Future amortization expense, 2019 | 842 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive
NBCUniversal Media, LLC [Member] |
Future amortization expense, 2015 | 777 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Future amortization expense, 2016 | 748 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Future amortization expense, 2017 | 747 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Future amortization expense, 2018 | 743 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Future amortization expense, 2019 | $ 740 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember

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- Definition Amount of amortization expense expected to be recognized during the next fiscal year following the latest fiscal year for assets, excluding financial assets and goodwill, lacking physical substance with a finite life. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Amount of amortization expense expected to be recognized during the fifth fiscal year following the latest fiscal year for assets, excluding financial assets and goodwill, lacking physical substance with a finite life. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Amount of amortization expense expected to be recognized during the fourth fiscal year following the latest fiscal year for assets, excluding financial assets and goodwill, lacking physical substance with a finite life. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275 + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | debit
Period Type: | instant

X
- Definition Amount of amortization expense expected to be recognized during the third fiscal year following the latest fiscal year for assets, excluding financial assets and goodwill, lacking physical substance with a finite life. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275 + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | debit
Period Type: | instant

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- Definition Amount of amortization expense expected to be recognized during the second fiscal year following the latest fiscal year for assets, excluding financial assets and goodwill, lacking physical substance with a finite life. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275 + Details
Name: | us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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