v2.4.1.9

Investments (Fair Value Method Investments) (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended
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Mar. 31, 2015
Prepaid forward sale liabilities carrying value | $ 0 cmcsa_LiabilitiesRelatedToPrepaidForwardSaleAgreements
Fair Value Equity Securities Settlement | $ 517 cmcsa_FairValueEquitySecuritiesSettlement

X
- Definition Fair value method equity securities used to settle our obligations under prepaid forward sale agreements in the period. + References No definition available. + Details
Name: | cmcsa_FairValueEquitySecuritiesSettlement
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The carrying value of the liabilities related to prepaid forward sale agreements. + References No definition available. + Details
Name: | cmcsa_LiabilitiesRelatedToPrepaidForwardSaleAgreements
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant