v2.4.1.9

Investments (Cost Method Investments) (Details) (USD $) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2014 | Dec. 31, 2013
Air Touch [Member] |  |
Fair value of AirTouch preferred stock related to redeemable preferred shares | $ 1,700,000,000 cmcsa_FairValueOfCostMethodInvestmentRedeemablePreferredShares / dei_LegalEntityAxis = cmcsa_AirTouchMember | $ 1,700,000,000 cmcsa_FairValueOfCostMethodInvestmentRedeemablePreferredShares / dei_LegalEntityAxis = cmcsa_AirTouchMember
Aggregate redemption value | 1,750,000,000 cmcsa_PreferredStockAggregateRedemptionValue / dei_LegalEntityAxis = cmcsa_AirTouchMember |
Carrying amount of redeemable preferred stock | 1,600,000,000 cmcsa_CarryingAmountOfRedeemablePreferredStock / dei_LegalEntityAxis = cmcsa_AirTouchMember | 1,500,000,000 cmcsa_CarryingAmountOfRedeemablePreferredStock / dei_LegalEntityAxis = cmcsa_AirTouchMember
Fair value of redeemable preferred stock | 1,700,000,000 cmcsa_FairValueAmountOfRedeemablePreferredStock / dei_LegalEntityAxis = cmcsa_AirTouchMember | 1,700,000,000 cmcsa_FairValueAmountOfRedeemablePreferredStock / dei_LegalEntityAxis = cmcsa_AirTouchMember
Nonredeemable preferred stock | 100,000,000 cmcsa_NonredeemablePreferredStock / dei_LegalEntityAxis = cmcsa_AirTouchMember | 100,000,000 cmcsa_NonredeemablePreferredStock / dei_LegalEntityAxis = cmcsa_AirTouchMember
Preferred Shares Redeemable in April 2020 [Member] |  |
Aggregate redemption value | $ 1,650,000,000 cmcsa_PreferredStockAggregateRedemptionValue / dei_LegalEntityAxis = cmcsa_PreferredSharesRedeemableInApril2020Member |

X
- Definition Carrying amount of redeemable preferred stock recorded in other noncurrent liabilities + 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: | debit
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

X
- Details
Name: | dei_LegalEntityAxis=cmcsa_AirTouchMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=cmcsa_PreferredSharesRedeemableInApril2020Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |