v2.4.0.6

Investments (Fair Value Method Investments) (Details) (USD $) In Billions, unless otherwise specified | 3 Months Ended
--- | ---
Jun. 30, 2012
Prepaid forward sale obligations carrying value | $ 2.9
Prepaid Forward Sale Obligations [Member] |
Equity securities held as collateral | 3.5
Prepaid forward sale obligations fair value | $ 3.0

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: | duration

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

X
- Definition The estimated fair value of our prepaid forward sale obligations. + References No definition available. + Details
Name: | cmcsa_PrepaidForwardSaleObligationsFairValue
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration