v2.4.1.9

Investments (Investment Income (Loss), Net) (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended
--- | ---
Mar. 31, 2015 | Mar. 31, 2014
Gains on sales and exchanges of investments, net | $ 0 us-gaap_RealizedInvestmentGainsLosses | $ 83 us-gaap_RealizedInvestmentGainsLosses
Investment impairment losses | (15)us-gaap_ImpairmentOfInvestments | (5)us-gaap_ImpairmentOfInvestments
Unrealized gains (losses) on securities underlying prepaid forward sale agreements | 42 us-gaap_UnrealizedGainLossOnSecurities | (113)us-gaap_UnrealizedGainLossOnSecurities
Mark to market adjustments on derivative component of prepaid forward sale agreements and indexed debt instruments | (38)cmcsa_MarkToMarketAdjustmentOnDerivativeComponentOfPrepaidForwardSaleAgreements | 117 cmcsa_MarkToMarketAdjustmentOnDerivativeComponentOfPrepaidForwardSaleAgreements
Interest and dividend income | 28 us-gaap_InvestmentIncomeInterestAndDividend | 28 us-gaap_InvestmentIncomeInterestAndDividend
Other, net | 16 cmcsa_OtherInvestmentIncomeLossNet | 3 cmcsa_OtherInvestmentIncomeLossNet
Investment income (loss), net | 33 us-gaap_InvestmentIncomeNonoperating | 113 us-gaap_InvestmentIncomeNonoperating
NBCUniversal Media, LLC [Member] |  |
Investment income (loss), net | $ (2)us-gaap_InvestmentIncomeNonoperating / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember | $ 6 us-gaap_InvestmentIncomeNonoperating / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember

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- Definition Mark To Market Adjustment on Derivative Component Of Prepaid Forward Sale Agreements and indexed debt instruments. + References No definition available. + Details
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- Definition Other Investment Income (Loss), net + References No definition available. + Details
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- 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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 35 -Paragraph 34 -URI http://asc.fasb.org/extlink&oid=27723805&loc=d3e25351-111560 + Details
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- Definition Amount before accretion (amortization) of purchase discount (premium) of interest income and dividend income on nonoperating securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.7(a),(b)) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 7 -Subparagraph a, b -Article 5 + Details
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- Definition The aggregate amount of income from investments (for example, dividends) not considered a component of the entity's core operations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.7) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 7 -Article 5 + Details
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- 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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.3(a)) -URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 325 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6485959&loc=d3e22529-158502 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 3 -Subparagraph a -Article 7 + Details
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- Definition Amount of unrealized gain (loss) recognized in the income statement on unsold other securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 + Details
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- Details
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