v2.4.1.9
Investments (Cost Method Investments) (Details) (Air Touch [Member], USD $)
Mar. 31, 2015
Air Touch [Member]
 
Fair value of AirTouch preferred stock related to redeemable preferred shares $ 1,700,000,000cmcsa_FairValueOfCostMethodInvestmentRedeemablePreferredShares
/ dei_LegalEntityAxis
= cmcsa_AirTouchMember
Fair value of redeemable preferred shares $ 1,700,000,000cmcsa_FairValueAmountOfRedeemablePreferredShares
/ dei_LegalEntityAxis
= cmcsa_AirTouchMember