v2.4.0.8

Investments (Fair Value Method Investments) (Details) (USD $) | 9 Months Ended |
--- | --- | ---
Sep. 30, 2014 | Dec. 31, 2013
Fair value equity securities held as collateral | $ 444,000,000 | $ 3,959,000,000
Obligations under prepaid forward sale agreements | 117,000,000 | 811,000,000
Derivative component of prepaid forward sale agreements | 277,000,000 | 2,800,000,000
Total liabilities associated with prepaid forward sale agreements | 394,000,000 | 3,611,000,000
Fair Value Equity Securities Settlement | $ 3,200,000,000 |

X
- Definition This element represents the fair value as of the balance sheet date of embedded derivative liabilities as a component of prepaid forward sale agreements valued on a recurring basis. + References No definition available. + Details
Name: | cmcsa_DerivativeFairValueOfEmbeddedDerivativeLiabilityComponentOfPrepaidForwardSaleAgreements
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Fair value method equity securities held as collateral related to our obligations under prepaid forward sale agreements. + References No definition available. + Details
Name: | cmcsa_EquitySecuritiesHeldAsCollateral
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

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