v2.4.1.9

Financial Data by Business Segment (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenue	$ 17,732,000,000us-gaap_Revenues	$ 16,791,000,000us-gaap_Revenues	$ 16,844,000,000us-gaap_Revenues	$ 17,408,000,000us-gaap_Revenues	$ 16,926,000,000us-gaap_Revenues	$ 16,151,000,000us-gaap_Revenues	$ 16,270,000,000us-gaap_Revenues	$ 15,310,000,000us-gaap_Revenues	$ 68,775,000,000us-gaap_Revenues	$ 64,657,000,000us-gaap_Revenues	$ 62,570,000,000us-gaap_Revenues
Operating income (loss) before depreciation and amortization									22,923,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization	21,434,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization	19,977,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization
Depreciation and amortization									8,019,000,000us-gaap_DepreciationAndAmortization	7,871,000,000us-gaap_DepreciationAndAmortization	7,798,000,000us-gaap_DepreciationAndAmortization
Operating income (loss)	3,787,000,000us-gaap_OperatingIncomeLoss	3,745,000,000us-gaap_OperatingIncomeLoss	3,804,000,000us-gaap_OperatingIncomeLoss	3,568,000,000us-gaap_OperatingIncomeLoss	3,647,000,000us-gaap_OperatingIncomeLoss	3,414,000,000us-gaap_OperatingIncomeLoss	3,435,000,000us-gaap_OperatingIncomeLoss	3,067,000,000us-gaap_OperatingIncomeLoss	14,904,000,000us-gaap_OperatingIncomeLoss	13,563,000,000us-gaap_OperatingIncomeLoss	12,179,000,000us-gaap_OperatingIncomeLoss
Capital expenditures									7,420,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment	6,596,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment	5,714,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment
Assets	159,339,000,000us-gaap_Assets				158,813,000,000us-gaap_Assets				159,339,000,000us-gaap_Assets	158,813,000,000us-gaap_Assets
NBCUniversal Media, LLC [Member]
Revenue									25,428,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	23,650,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	23,812,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Operating income (loss) before depreciation and amortization									5,588,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	4,732,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	4,107,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Depreciation and amortization									1,495,000,000us-gaap_DepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	1,411,000,000us-gaap_DepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	1,326,000,000us-gaap_DepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Operating income (loss)									4,093,000,000us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	3,321,000,000us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	2,781,000,000us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Capital expenditures									1,221,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	1,160,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	763,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Assets	52,617,000,000us-gaap_Assets / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember				51,739,000,000us-gaap_Assets / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember				52,617,000,000us-gaap_Assets / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	51,739,000,000us-gaap_Assets / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Non U S Customers [Member]
Revenue									4,400,000,000us-gaap_Revenues / us-gaap_StatementGeographicalAxis = cmcsa_NonUSCustomersMember	4,800,000,000us-gaap_Revenues / us-gaap_StatementGeographicalAxis = cmcsa_NonUSCustomersMember	4,500,000,000us-gaap_Revenues / us-gaap_StatementGeographicalAxis = cmcsa_NonUSCustomersMember
Non U S Customers [Member] | NBCUniversal Media, LLC [Member]
Revenue									4,433,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementGeographicalAxis = cmcsa_NonUSCustomersMember	4,763,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementGeographicalAxis = cmcsa_NonUSCustomersMember	4,464,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementGeographicalAxis = cmcsa_NonUSCustomersMember
United States [Member] | NBCUniversal Media, LLC [Member]
Revenue									20,995,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementGeographicalAxis = cmcsa_UnitedStatesMember	18,887,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementGeographicalAxis = cmcsa_UnitedStatesMember	19,348,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementGeographicalAxis = cmcsa_UnitedStatesMember
Cable Communications [Member]
Revenue									44,140,000,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableCommunicationsMember	41,836,000,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableCommunicationsMember	39,604,000,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableCommunicationsMember
Operating income (loss) before depreciation and amortization									18,112,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableCommunicationsMember	17,205,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableCommunicationsMember	16,255,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableCommunicationsMember
Depreciation and amortization									6,422,000,000us-gaap_DepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableCommunicationsMember	6,394,000,000us-gaap_DepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableCommunicationsMember	6,405,000,000us-gaap_DepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableCommunicationsMember
Operating income (loss)									11,690,000,000us-gaap_OperatingIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableCommunicationsMember	10,811,000,000us-gaap_OperatingIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableCommunicationsMember	9,850,000,000us-gaap_OperatingIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableCommunicationsMember
Capital expenditures									6,154,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableCommunicationsMember	5,403,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableCommunicationsMember	4,921,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableCommunicationsMember
Cable segment revenue types as percentage of total cable revenue									100.00%cmcsa_CableSegmentRevenueTypesAsPercentageOfTotalCableRevenue / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableCommunicationsMember	100.00%cmcsa_CableSegmentRevenueTypesAsPercentageOfTotalCableRevenue / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableCommunicationsMember	100.00%cmcsa_CableSegmentRevenueTypesAsPercentageOfTotalCableRevenue / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableCommunicationsMember
Assets	140,616,000,000us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableCommunicationsMember				132,082,000,000us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableCommunicationsMember				140,616,000,000us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableCommunicationsMember	132,082,000,000us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableCommunicationsMember
Cable Networks [Member]
Revenue									9,563,000,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember	9,201,000,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember	8,727,000,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember
Operating income (loss) before depreciation and amortization									3,589,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember	3,501,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember	3,303,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember
Depreciation and amortization									748,000,000us-gaap_DepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember	734,000,000us-gaap_DepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember	735,000,000us-gaap_DepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember
Operating income (loss)									2,841,000,000us-gaap_OperatingIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember	2,767,000,000us-gaap_OperatingIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember	2,568,000,000us-gaap_OperatingIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember
Capital expenditures									49,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember	67,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember	150,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember
Assets	28,582,000,000us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember				29,413,000,000us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember				28,582,000,000us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember	29,413,000,000us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember
Cable Networks [Member] | NBCUniversal Media, LLC [Member]
Revenue									9,563,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember	9,201,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember	8,727,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember
Operating income (loss) before depreciation and amortization									3,589,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember	3,501,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember	3,303,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember
Depreciation and amortization									748,000,000us-gaap_DepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember	734,000,000us-gaap_DepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember	735,000,000us-gaap_DepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember
Operating income (loss)									2,841,000,000us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember	2,767,000,000us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember	2,568,000,000us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember
Capital expenditures									49,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember	67,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember	150,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember
Assets	28,582,000,000us-gaap_Assets / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember				29,413,000,000us-gaap_Assets / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember				28,582,000,000us-gaap_Assets / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember	29,413,000,000us-gaap_Assets / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_CableNetworksMember
Broadcast Television [Member]
Revenue									8,542,000,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember	7,120,000,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember	8,200,000,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember
Operating income (loss) before depreciation and amortization									734,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember	345,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember	358,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember
Depreciation and amortization									127,000,000us-gaap_DepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember	98,000,000us-gaap_DepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember	97,000,000us-gaap_DepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember
Operating income (loss)									607,000,000us-gaap_OperatingIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember	247,000,000us-gaap_OperatingIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember	261,000,000us-gaap_OperatingIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember
Capital expenditures									76,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember	65,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember	65,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember
Assets	6,806,000,000us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember				6,723,000,000us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember				6,806,000,000us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember	6,723,000,000us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember
Broadcast Television [Member] | NBCUniversal Media, LLC [Member]
Revenue									8,542,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember	7,120,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember	8,200,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember
Operating income (loss) before depreciation and amortization									734,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember	345,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember	358,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember
Depreciation and amortization									127,000,000us-gaap_DepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember	98,000,000us-gaap_DepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember	97,000,000us-gaap_DepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember
Operating income (loss)									607,000,000us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember	247,000,000us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember	261,000,000us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember
Capital expenditures									76,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember	65,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember	65,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember
Assets	6,806,000,000us-gaap_Assets / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember				6,723,000,000us-gaap_Assets / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember				6,806,000,000us-gaap_Assets / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember	6,723,000,000us-gaap_Assets / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_BroadcastTelevisionMember
Filmed Entertainment [Member]
Revenue									5,008,000,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember	5,452,000,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember	5,159,000,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember
Operating income (loss) before depreciation and amortization									711,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember	483,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember	79,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember
Depreciation and amortization									21,000,000us-gaap_DepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember	15,000,000us-gaap_DepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember	16,000,000us-gaap_DepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember
Operating income (loss)									690,000,000us-gaap_OperatingIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember	468,000,000us-gaap_OperatingIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember	63,000,000us-gaap_OperatingIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember
Capital expenditures									11,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember	9,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember	7,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember
Assets	4,185,000,000us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember				3,549,000,000us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember				4,185,000,000us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember	3,549,000,000us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember
Filmed Entertainment [Member] | NBCUniversal Media, LLC [Member]
Revenue									5,008,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember	5,452,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember	5,159,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember
Operating income (loss) before depreciation and amortization									711,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember	483,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember	79,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember
Depreciation and amortization									21,000,000us-gaap_DepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember	15,000,000us-gaap_DepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember	16,000,000us-gaap_DepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember
Operating income (loss)									690,000,000us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember	468,000,000us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember	63,000,000us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember
Capital expenditures									11,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember	9,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember	7,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember
Assets	4,185,000,000us-gaap_Assets / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember				3,549,000,000us-gaap_Assets / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember				4,185,000,000us-gaap_Assets / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember	3,549,000,000us-gaap_Assets / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_FilmedEntertainmentMember
Theme Parks [Member]
Revenue									2,623,000,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember	2,235,000,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember	2,085,000,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember
Operating income (loss) before depreciation and amortization									1,168,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember	1,004,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember	953,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember
Depreciation and amortization									273,000,000us-gaap_DepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember	300,000,000us-gaap_DepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember	268,000,000us-gaap_DepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember
Operating income (loss)									895,000,000us-gaap_OperatingIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember	704,000,000us-gaap_OperatingIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember	685,000,000us-gaap_OperatingIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember
Capital expenditures									671,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember	580,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember	272,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember
Assets	7,017,000,000us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember				6,608,000,000us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember				7,017,000,000us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember	6,608,000,000us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember
Theme Parks [Member] | NBCUniversal Media, LLC [Member]
Revenue									2,623,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember	2,235,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember	2,085,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember
Operating income (loss) before depreciation and amortization									1,168,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember	1,004,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember	953,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember
Depreciation and amortization									273,000,000us-gaap_DepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember	300,000,000us-gaap_DepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember	268,000,000us-gaap_DepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember
Operating income (loss)									895,000,000us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember	704,000,000us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember	685,000,000us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember
Capital expenditures									671,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember	580,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember	272,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember
Assets	7,017,000,000us-gaap_Assets / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember				6,608,000,000us-gaap_Assets / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember				7,017,000,000us-gaap_Assets / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember	6,608,000,000us-gaap_Assets / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_ThemeParksMember
Headquarters And Other [Member]
Revenue									13,000,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember	31,000,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember	43,000,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember
Operating income (loss) before depreciation and amortization									(613,000,000)cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember	(588,000,000)cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember	(603,000,000)cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember
Depreciation and amortization									326,000,000us-gaap_DepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember	264,000,000us-gaap_DepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember	210,000,000us-gaap_DepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember
Operating income (loss)									(939,000,000)us-gaap_OperatingIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember	(852,000,000)us-gaap_OperatingIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember	(813,000,000)us-gaap_OperatingIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember
Capital expenditures									414,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember	439,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember	269,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember
Assets	6,479,000,000us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember				6,002,000,000us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember				6,479,000,000us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember	6,002,000,000us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember
Headquarters And Other [Member] | NBCUniversal Media, LLC [Member]
Revenue									13,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember	31,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember	43,000,000us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember
Operating income (loss) before depreciation and amortization									(613,000,000)cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember	(588,000,000)cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember	(603,000,000)cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember
Depreciation and amortization									326,000,000us-gaap_DepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember	264,000,000us-gaap_DepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember	210,000,000us-gaap_DepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember
Operating income (loss)									(939,000,000)us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember	(852,000,000)us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember	(813,000,000)us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember
Capital expenditures									414,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember	439,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember	269,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember
Assets	6,479,000,000us-gaap_Assets / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember				6,002,000,000us-gaap_Assets / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember				6,479,000,000us-gaap_Assets / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember	6,002,000,000us-gaap_Assets / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_HeadquartersAndOtherMember
NBCUniversal Eliminations [Member]
Revenue									(321,000,000)us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember	(389,000,000)us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember	(402,000,000)us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember
Operating income (loss) before depreciation and amortization									(1,000,000)cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember	(13,000,000)cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember	17,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember
Depreciation and amortization									0us-gaap_DepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember	0us-gaap_DepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember	0us-gaap_DepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember
Operating income (loss)									(1,000,000)us-gaap_OperatingIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember	(13,000,000)us-gaap_OperatingIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember	17,000,000us-gaap_OperatingIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember
Capital expenditures									0us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember	0us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember	0us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember
Assets	(452,000,000)us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember				(556,000,000)us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember				(452,000,000)us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember	(556,000,000)us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember
NBCUniversal Eliminations [Member] | NBCUniversal Media, LLC [Member]
Revenue									(321,000,000)us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember	(389,000,000)us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember	(402,000,000)us-gaap_Revenues / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember
Operating income (loss) before depreciation and amortization									(1,000,000)cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember	(13,000,000)cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember	17,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember
Depreciation and amortization									0us-gaap_DepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember	0us-gaap_DepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember	0us-gaap_DepreciationAndAmortization / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember
Operating income (loss)									(1,000,000)us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember	(13,000,000)us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember	17,000,000us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember
Capital expenditures									0us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember	0us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember	0us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember
Assets	(452,000,000)us-gaap_Assets / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember				(556,000,000)us-gaap_Assets / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember				(452,000,000)us-gaap_Assets / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember	(556,000,000)us-gaap_Assets / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalEliminationsMember
NBCUniversal [Member]
Revenue									25,428,000,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalMember	23,650,000,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalMember	23,812,000,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalMember
Operating income (loss) before depreciation and amortization									5,588,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalMember	4,732,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalMember	4,107,000,000cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalMember
Depreciation and amortization									1,495,000,000us-gaap_DepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalMember	1,411,000,000us-gaap_DepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalMember	1,326,000,000us-gaap_DepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalMember
Operating income (loss)									4,093,000,000us-gaap_OperatingIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalMember	3,321,000,000us-gaap_OperatingIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalMember	2,781,000,000us-gaap_OperatingIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalMember
Capital expenditures									1,221,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalMember	1,160,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalMember	763,000,000us-gaap_PaymentsToAcquirePropertyPlantAndEquipment / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalMember
Assets	52,617,000,000us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalMember				51,739,000,000us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalMember				52,617,000,000us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalMember	51,739,000,000us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = cmcsa_NbcuniversalMember
Corporate and Other [Member]
Revenue									709,000,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = us-gaap_CorporateAndOtherMember	600,000,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = us-gaap_CorporateAndOtherMember	498,000,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = us-gaap_CorporateAndOtherMember
Operating income (loss) before depreciation and amortization									(778,000,000)cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = us-gaap_CorporateAndOtherMember	(489,000,000)cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = us-gaap_CorporateAndOtherMember	(376,000,000)cmcsa_OperatingIncomeExcludingDepreciationAndAmortization / us-gaap_StatementBusinessSegmentsAxis = us-gaap_CorporateAndOtherMember
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Cable Communications Segment Revenue Percentage - High-speed Internet [Member]
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Cable Communications Segment Revenue Percentage- Voice [Member]
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Cable Communications Segment Revenue Percentage- Business Services [Member]
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Cable Communications Segment Revenue Percentage- Advertising [Member]
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Cable Communications Segment Revenue Percentage- Other [Member]
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Cable Communications Segment Revenue Percentage- Franchise and other regulatory fees [Member]
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