v3.3.1.900

Recent Accounting Pronouncements (Narrative) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2015 | Dec. 31, 2014
Debt issuance cost | $ 176 |
NBCUniversal Media LLC [Member] |  |
Debt issuance cost | $ 11 |
Debt Issuance Costs New Account Pronouncement - Reduction of Long Term Debt [Member] |  |
New accounting pronouncement, early adoption, effect on balance sheet |  | $ 153
Debt Issuance Costs New Account Pronouncement - Reduction of Long Term Debt [Member] | NBCUniversal Media LLC [Member] |  |
New accounting pronouncement, early adoption, effect on balance sheet |  | 12
Deferred Income Taxes New Accounting Pronouncement Reclass to Long Term Liabilities [Member] |  |
New Accounting Pronouncement, early adoption, effect on balance sheet if retrospectively adopted |  | $ 195

X
- Definition Represents the amount that was reclassified on the balance sheet as a result of early adopting the new accounting standard, either prospectively or retrospectively. + References No definition available. + Details
Name: | cmcsa_NewAccountingPronouncementEffectiveAdoptionImpactOnBalanceSheet
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Represents the amount that would have been reclassified on the balance sheet as a result of early adopting the new accounting standard, either prospectively or retrospectively. + References No definition available. + Details
Name: | cmcsa_NewAccountingPronouncementImpactOnBalanceSheetIfRetrospectivelyAdopted
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of debt issuance costs (for example, but not limited to, legal, accounting, broker, and regulatory fees). + References No definition available. + Details
Name: | us-gaap_DebtIssuanceCosts
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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

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

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