v2.4.1.9

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

X
- Definition Fair value of our redeemable subsidiary preferred shares and/or stock + References No definition available. + Details
Name: | cmcsa_FairValueAmountOfRedeemablePreferredShares
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The fair value of a cost method investment related to redeemable preferred shares. + References No definition available. + Details
Name: | cmcsa_FairValueOfCostMethodInvestmentRedeemablePreferredShares
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant