v2.4.1.9

Condensed Consolidated Balance Sheet (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Preferred stock, authorized	20,000,000us-gaap_PreferredStockSharesAuthorized	20,000,000us-gaap_PreferredStockSharesAuthorized
Preferred stock, issued	0us-gaap_PreferredStockSharesIssued	0us-gaap_PreferredStockSharesIssued
Accumulated depreciation	$ 46,037us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment	$ 45,410us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment
Accumulated amortization	10,507us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization	10,170us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization
NBCUniversal Media, LLC [Member]
Accumulated depreciation	2,309us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	2,167us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Accumulated amortization	$ 5,027us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	$ 4,829us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Class A Common Stock [Member]
Common stock, par value	$ 0.01us-gaap_CommonStockParOrStatedValuePerShare / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassAMember	$ 0.01us-gaap_CommonStockParOrStatedValuePerShare / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassAMember
Common stock, authorized	7,500,000,000us-gaap_CommonStockSharesAuthorized / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassAMember	7,500,000,000us-gaap_CommonStockSharesAuthorized / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassAMember
Common stock, issued	2,488,377,059us-gaap_CommonStockSharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassAMember	2,496,598,612us-gaap_CommonStockSharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassAMember
Common stock, outstanding	2,122,916,309us-gaap_CommonStockSharesOutstanding / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassAMember	2,131,137,862us-gaap_CommonStockSharesOutstanding / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassAMember
Treasury stock common shares	365,460,750us-gaap_TreasuryStockShares / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassAMember	365,460,750us-gaap_TreasuryStockShares / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassAMember
Class A Special Common Stock [Member]
Common stock, par value	$ 0.01us-gaap_CommonStockParOrStatedValuePerShare / us-gaap_StatementClassOfStockAxis = cmcsa_ClassaSpecialCommonStockMember	$ 0.01us-gaap_CommonStockParOrStatedValuePerShare / us-gaap_StatementClassOfStockAxis = cmcsa_ClassaSpecialCommonStockMember
Common stock, authorized	7,500,000,000us-gaap_CommonStockSharesAuthorized / us-gaap_StatementClassOfStockAxis = cmcsa_ClassaSpecialCommonStockMember	7,500,000,000us-gaap_CommonStockSharesAuthorized / us-gaap_StatementClassOfStockAxis = cmcsa_ClassaSpecialCommonStockMember
Common stock, issued	452,117,242us-gaap_CommonStockSharesIssued / us-gaap_StatementClassOfStockAxis = cmcsa_ClassaSpecialCommonStockMember	471,419,601us-gaap_CommonStockSharesIssued / us-gaap_StatementClassOfStockAxis = cmcsa_ClassaSpecialCommonStockMember
Common stock, outstanding	381,182,478us-gaap_CommonStockSharesOutstanding / us-gaap_StatementClassOfStockAxis = cmcsa_ClassaSpecialCommonStockMember	400,484,837us-gaap_CommonStockSharesOutstanding / us-gaap_StatementClassOfStockAxis = cmcsa_ClassaSpecialCommonStockMember
Treasury stock common shares	70,934,764us-gaap_TreasuryStockShares / us-gaap_StatementClassOfStockAxis = cmcsa_ClassaSpecialCommonStockMember	70,934,764us-gaap_TreasuryStockShares / us-gaap_StatementClassOfStockAxis = cmcsa_ClassaSpecialCommonStockMember
Class B Common Stock [Member]
Common stock, par value	$ 0.01us-gaap_CommonStockParOrStatedValuePerShare / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassBMember	$ 0.01us-gaap_CommonStockParOrStatedValuePerShare / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassBMember
Common stock, authorized	75,000,000us-gaap_CommonStockSharesAuthorized / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassBMember	75,000,000us-gaap_CommonStockSharesAuthorized / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassBMember
Common stock, issued	9,444,375us-gaap_CommonStockSharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassBMember	9,444,375us-gaap_CommonStockSharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassBMember
Common stock, outstanding	9,444,375us-gaap_CommonStockSharesOutstanding / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassBMember	9,444,375us-gaap_CommonStockSharesOutstanding / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassBMember

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