v2.4.1.9

Film and Television Costs (Narrative)(Details) (USD $) | Dec. 31, 2014
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Amortization of completed film and television production expected to be amortized during the next fiscal year | $ 1,300,000,000 cmcsa_AmortizationOfOriginalFilmAndTelevisionProductionExpectedToBeAmortizedDuringNextFiscalYear
Expected amortization percentage of released and unamortized film and television costs | 86.00%cmcsa_ExpectedAmortizationPercentageOfCompletedNotReleasedAndUnamortizedFilmAndTelevisionCosts
Remaining unamortized costs of acquired film and television libraries | 570,000,000 cmcsa_FilmAndTelevisionLibraryCostsUnamortized
Expected amortization percentage of unamortized film and television library costs during the next three fiscal years | 51.00%cmcsa_PercentageOfAcquiredFilmAndTelevisionLibrariesToBeAmortizedInNextThreeYears
NBCUniversal Media, LLC [Member] |
Amortization of completed film and television production expected to be amortized during the next fiscal year | 1,300,000,000 cmcsa_AmortizationOfOriginalFilmAndTelevisionProductionExpectedToBeAmortizedDuringNextFiscalYear / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Expected amortization percentage of released and unamortized film and television costs | 86.00%cmcsa_ExpectedAmortizationPercentageOfCompletedNotReleasedAndUnamortizedFilmAndTelevisionCosts / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Remaining unamortized costs of acquired film and television libraries | $ 570,000,000 cmcsa_FilmAndTelevisionLibraryCostsUnamortized / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Expected amortization percentage of unamortized film and television library costs during the next three fiscal years | 51.00%cmcsa_PercentageOfAcquiredFilmAndTelevisionLibrariesToBeAmortizedInNextThreeYears / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember

X
- Definition The amount of film and television costs related to completed film and television productions, excluding acquired libraries, that are expected to be amortized during the upcoming operating cycle. + References No definition available. + Details
Name: | cmcsa_AmortizationOfOriginalFilmAndTelevisionProductionExpectedToBeAmortizedDuringNextFiscalYear
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The percentage of unamortized film costs for released films and television costs, excluding acquired film libraries, expected to be amortized within three years from the date of the balance sheet. + References No definition available. + Details
Name: | cmcsa_ExpectedAmortizationPercentageOfCompletedNotReleasedAndUnamortizedFilmAndTelevisionCosts
Namespace Prefix: | cmcsa_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The remaining amount of costs related to film and television libraries that are expected to be amortized. + References No definition available. + Details
Name: | cmcsa_FilmAndTelevisionLibraryCostsUnamortized
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The percentage of unamortized film and television library costs that are expected to be amortized within three years from the date of the balance sheet. + References No definition available. + Details
Name: | cmcsa_PercentageOfAcquiredFilmAndTelevisionLibrariesToBeAmortizedInNextThreeYears
Namespace Prefix: | cmcsa_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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