v3.3.1.900

Pension Plans and Postretirement Benefits (Deferred Compensation Plans) (Details) - Deferred Compensation Plans [Member] - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Benefit obligation | $ 2,038 | $ 1,774 | $ 1,434
Interest expense | 171 | 149 | 128
NBCUniversal Media LLC [Member] |  |  |
Benefit obligation | 417 | 349 | 250
Interest expense | $ 28 | $ 24 | $ 18

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- Definition Deferred compensation plans benefit obligation + References No definition available. + Details
Name: | cmcsa_DeferredCompensationPlansBenefitObligation
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- 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

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- Details
Name: | us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis=cmcsa_DeferredCompensationPlansMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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