v2.4.1.9

Pension Plans and Postretirement Benefits (Deferred Compensation Plans) (Details) (Deferred Compensation Plans [Member], USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Benefit obligation | $ 1,774 us-gaap_DeferredCompensationLiabilityCurrentAndNoncurrent | $ 1,434 us-gaap_DeferredCompensationLiabilityCurrentAndNoncurrent | $ 1,247 us-gaap_DeferredCompensationLiabilityCurrentAndNoncurrent
Interest expense | 149 cmcsa_DeferredCompensationPlansInterestCost | 128 cmcsa_DeferredCompensationPlansInterestCost | 107 cmcsa_DeferredCompensationPlansInterestCost
NBCUniversal Media, LLC [Member] |  |  |
Benefit obligation | 349 us-gaap_DeferredCompensationLiabilityCurrentAndNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cmcsa_DeferredCompensationPlansMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | 250 us-gaap_DeferredCompensationLiabilityCurrentAndNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cmcsa_DeferredCompensationPlansMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | 163 us-gaap_DeferredCompensationLiabilityCurrentAndNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cmcsa_DeferredCompensationPlansMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Interest expense | $ 24 cmcsa_DeferredCompensationPlansInterestCost / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cmcsa_DeferredCompensationPlansMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | $ 18 cmcsa_DeferredCompensationPlansInterestCost / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cmcsa_DeferredCompensationPlansMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | $ 11 cmcsa_DeferredCompensationPlansInterestCost / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cmcsa_DeferredCompensationPlansMember / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember

X
- Definition Deferred compensation plans interest cost + References No definition available. + Details
Name: | cmcsa_DeferredCompensationPlansInterestCost
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Aggregate carrying value as of the balance sheet date of the liabilities for all deferred compensation arrangements. Represents currently earned compensation under compensation arrangements that is not actually paid until a later date. + References No definition available. + Details
Name: | us-gaap_DeferredCompensationLiabilityCurrentAndNoncurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant