v2.4.1.9
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, 2014
Dec. 31, 2013
Dec. 31, 2012
Postretirement and Pension Plans      
Benefit obligation $ 217cmcsa_SplitDollarLifeInsuranceAgreementsBenefitObligation $ 212cmcsa_SplitDollarLifeInsuranceAgreementsBenefitObligation $ 202cmcsa_SplitDollarLifeInsuranceAgreementsBenefitObligation
Other operating and administrative expenses $ 52cmcsa_SplitDollarLifeInsuranceAgreementExpense $ 50cmcsa_SplitDollarLifeInsuranceAgreementExpense $ 58cmcsa_SplitDollarLifeInsuranceAgreementExpense