v2.4.0.8

Pension Plans and Postretirement Benefits (Benefit Obligation and Expense for Our Split-Dollar Life Insurance Agreements) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011
Benefit obligation | $ 212 | $ 202 | $ 169
Other operating and administrative expenses | $ 50 | $ 58 | $ 27

X
- Definition Split Dollar Life Insurance Agreement Expense + References No definition available. + Details
Name: | cmcsa_SplitDollarLifeInsuranceAgreementExpense
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Split-dollar life insurance agreements benefit obligation + References No definition available. + Details
Name: | cmcsa_SplitDollarLifeInsuranceAgreementsBenefitObligation
Namespace Prefix: | cmcsa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration