|
Investments (Investment Income (Loss), Net) (Details) (USD $)
In Millions, unless otherwise specified |
12 Months Ended | ||
|---|---|---|---|
|
Dec. 31, 2014
|
Dec. 31, 2013
|
Dec. 31, 2012
|
|
| Gains on sales and exchanges of investments, net | $ 192us-gaap_RealizedInvestmentGainsLosses | $ 484us-gaap_RealizedInvestmentGainsLosses | $ 30us-gaap_RealizedInvestmentGainsLosses |
| Investment impairment losses | (50)us-gaap_ImpairmentOfInvestments | (29)us-gaap_ImpairmentOfInvestments | (24)us-gaap_ImpairmentOfInvestments |
| Unrealized gains on securities underlying prepaid forward sale agreements | 66us-gaap_UnrealizedGainLossOnSecurities | 1,601us-gaap_UnrealizedGainLossOnSecurities | 1,159us-gaap_UnrealizedGainLossOnSecurities |
| Mark to market adjustments on derivative component of prepaid forward sale agreements and indexed debt instruments | (56)cmcsa_MarkToMarketAdjustmentOnDerivativeComponentOfPrepaidForwardSaleAgreements | (1,604)cmcsa_MarkToMarketAdjustmentOnDerivativeComponentOfPrepaidForwardSaleAgreements | (1,071)cmcsa_MarkToMarketAdjustmentOnDerivativeComponentOfPrepaidForwardSaleAgreements |
| Interest and dividend income | 116us-gaap_InvestmentIncomeInterestAndDividend | 111us-gaap_InvestmentIncomeInterestAndDividend | 119us-gaap_InvestmentIncomeInterestAndDividend |
| Other, net | 28cmcsa_OtherInvestmentIncomeLossNet | 13cmcsa_OtherInvestmentIncomeLossNet | 6cmcsa_OtherInvestmentIncomeLossNet |
| Investment income (loss), net | 296us-gaap_InvestmentIncomeNonoperating | 576us-gaap_InvestmentIncomeNonoperating | 219us-gaap_InvestmentIncomeNonoperating |
| NBCUniversal Media, LLC [Member] | |||
| Investment income (loss), net | $ 27us-gaap_InvestmentIncomeNonoperating / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember |
$ 17us-gaap_InvestmentIncomeNonoperating / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember |
$ 27us-gaap_InvestmentIncomeNonoperating / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember |
| X | ||||||||||
|
- Definition
Mark To Market Adjustment on Derivative Component Of Prepaid Forward Sale Agreements and indexed debt instruments. No definition available.
|
| X | ||||||||||
|
- Definition
Other Investment Income (Loss), net No definition available.
|
| X | ||||||||||
|
- Definition
The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|
| X | ||||||||||
|
- Definition
Amount before accretion (amortization) of purchase discount (premium) of interest income and dividend income on nonoperating securities. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|
| X | ||||||||||
|
- Definition
The aggregate amount of income from investments (for example, dividends) not considered a component of the entity's core operations. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|
| X | ||||||||||
|
- Definition
The net realized gains or losses on investments during the period, not including gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|
| X | ||||||||||
|
- Definition
Amount of unrealized gain (loss) recognized in the income statement on unsold other securities. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|
| X | ||||||||||
|
- Details
|