v3.5.0.2

Recent Accounting Pronouncements (Narrative) (Details) - Share Based Compensation New Accounting Pronouncement [Member] - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
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Jun. 30, 2016 | Jun. 30, 2016
New Accounting Pronouncement, effect on income statement | $ 48 | $ 159
New Accounting Pronouncement, effect on statement of cash flow |  | $ 411

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- Definition Represents the amount that would have increased (decreased) our net income attributable to the parent if the new accounting standard was adopted + References No definition available. + Details
Name: | cmcsa_NewAccountingPronouncementImpactOnIncomeStatementIfAdopted
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Represents the amount that would have increased net cash provided by operating activities and decreased net cash provided by (used in) financing activities if the new accounting standard was adopted + References No definition available. + Details
Name: | cmcsa_NewAccountingPronouncementImpactOnStatementOfCashFlowIfAdopted
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Details
Name: | us-gaap_NewAccountingPronouncementEarlyAdoptionAxis=cmcsa_ShareBasedCompensationNewAccountingPronouncementMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |