v2.4.1.9
Film and Television Costs (Narrative)(Details) (USD $)
Dec. 31, 2014
Amortization of completed film and television production expected to be amortized during the next fiscal year $ 1,300,000,000cmcsa_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 570,000,000cmcsa_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 1,300,000,000cmcsa_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 $ 570,000,000cmcsa_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