v2.4.0.8

Investments (Cost Method Investments) (Details) (USD $) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2013 | Dec. 31, 2012
Air Touch [Member] |  |
Fair value of AirTouch preferred stock related to redeemable preferred shares | $ 1,700,000,000 | $ 1,800,000,000
Aggregate redemption value | 1,750,000,000 |
Carrying amount of redeemable preferred stock | 1,500,000,000 | 1,500,000,000
Fair value amount of redeemable preferred stock | 1,700,000,000 | 1,800,000,000
Nonredeemable preferred stock | 100,000,000 | 100,000,000
Preferred Shares Redeemable in April 2020 [Member] |  |
Aggregate redemption value | $ 1,650,000,000 |

X
- Definition Carrying amount of redeemable preferred stock + References No definition available. + Details
Name: | cmcsa_CarryingAmountOfRedeemablePreferredStock
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Fair value of our redeemable subsidiary preferred stock. + References No definition available. + Details
Name: | cmcsa_FairValueAmountOfRedeemablePreferredStock
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: | credit
Period Type: | instant

X
- Definition Nonredeemable preferred stock issued by a wholly owned subsidiary of the company. + References No definition available. + Details
Name: | cmcsa_NonredeemablePreferredStock
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Preferred stock aggregate redemption value + References No definition available. + Details
Name: | cmcsa_PreferredStockAggregateRedemptionValue
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration