v2.4.1.9

Property and Equipment (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2014
Cable distribution system	$ 30,498,000,000cmcsa_CableDistributionSystems	$ 31,655,000,000cmcsa_CableDistributionSystems
Customer premise equipment	25,949,000,000cmcsa_CustomerPremiseEquipment	27,086,000,000cmcsa_CustomerPremiseEquipment
Other equipment	6,826,000,000us-gaap_PropertyPlantAndEquipmentOther	7,860,000,000us-gaap_PropertyPlantAndEquipmentOther
Buildings and leasehold improvements	8,057,000,000us-gaap_BuildingsAndImprovementsGross	8,650,000,000us-gaap_BuildingsAndImprovementsGross
Land	1,084,000,000us-gaap_Land	1,112,000,000us-gaap_Land
Property and equipment, at cost	72,414,000,000us-gaap_PropertyPlantAndEquipmentGross	76,363,000,000us-gaap_PropertyPlantAndEquipmentGross
Less: Accumulated depreciation	42,574,000,000us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment	45,410,000,000us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment
Property and equipment, net	29,840,000,000us-gaap_PropertyPlantAndEquipmentNet	30,953,000,000us-gaap_PropertyPlantAndEquipmentNet
NBCUniversal Media, LLC [Member]
Buildings and leasehold improvements	5,239,000,000us-gaap_BuildingsAndImprovementsGross / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	5,780,000,000us-gaap_BuildingsAndImprovementsGross / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Land	799,000,000us-gaap_Land / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	820,000,000us-gaap_Land / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Furniture, fixtures and equipment	2,383,000,000us-gaap_FurnitureAndFixturesGross / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	2,930,000,000us-gaap_FurnitureAndFixturesGross / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Construction in process	828,000,000us-gaap_ConstructionInProgressGross / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	775,000,000us-gaap_ConstructionInProgressGross / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Property and equipment, at cost	9,249,000,000us-gaap_PropertyPlantAndEquipmentGross / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	10,305,000,000us-gaap_PropertyPlantAndEquipmentGross / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Less: Accumulated depreciation	1,599,000,000us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	2,167,000,000us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Property and equipment, net	7,650,000,000us-gaap_PropertyPlantAndEquipmentNet / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember	8,138,000,000us-gaap_PropertyPlantAndEquipmentNet / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember
Cable Distribution System [Member]
Weighted average original useful life (in years)		11cmcsa_WeightedAverageOriginalUsefulLife / us-gaap_PropertyPlantAndEquipmentByTypeAxis = cmcsa_CableDistributionSystemMember
Customer Premise Equipment [Member]
Weighted average original useful life (in years)		6cmcsa_WeightedAverageOriginalUsefulLife / us-gaap_PropertyPlantAndEquipmentByTypeAxis = cmcsa_CustomerPremiseEquipmentMember
Other Equipment [Member]
Weighted average original useful life (in years)		6cmcsa_WeightedAverageOriginalUsefulLife / us-gaap_PropertyPlantAndEquipmentByTypeAxis = us-gaap_OtherCapitalizedPropertyPlantAndEquipmentMember
Buildings and Leasehold Improvements [Member]
Weighted average original useful life (in years)		22cmcsa_WeightedAverageOriginalUsefulLife / us-gaap_PropertyPlantAndEquipmentByTypeAxis = us-gaap_BuildingAndBuildingImprovementsMember
Buildings and Leasehold Improvements [Member] | NBCUniversal Media, LLC [Member]
Weighted average original useful life (in years)		21cmcsa_WeightedAverageOriginalUsefulLife / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_PropertyPlantAndEquipmentByTypeAxis = us-gaap_BuildingAndBuildingImprovementsMember
Furniture Fixtures And Equipment [Member] | NBCUniversal Media, LLC [Member]
Weighted average original useful life (in years)		7cmcsa_WeightedAverageOriginalUsefulLife / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_PropertyPlantAndEquipmentByTypeAxis = us-gaap_FurnitureAndFixturesMember
Comcast Center [Member]
Equity interest acquired	80.00%us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired / us-gaap_PropertyPlantAndEquipmentByTypeAxis = cmcsa_ComcastCenterMember
Acquisition Of Real Estate Properties [Member]
Increases in property and equpiment related to real estate acquisitions	2,200,000,000us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_PropertyPlantAndEquipmentByTypeAxis = cmcsa_AcquisitionOfRealEstatePropertiesMember
Acquisition Of Real Estate Properties [Member] | NBCUniversal Media, LLC [Member]
Increases in property and equpiment related to real estate acquisitions	$ 1,700,000,000us-gaap_PropertyPlantAndEquipmentAdditions / dei_LegalEntityAxis = cmcsa_NBCUniversalMediaLLCMember / us-gaap_PropertyPlantAndEquipmentByTypeAxis = cmcsa_AcquisitionOfRealEstatePropertiesMember

X

- Definition

Costs associated with the construction of and improvements to our cable transmission and distribution facilities.

+ References

No definition available.

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- Definition

The cost of customer premises equipment.

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- Definition

The weighted average original useful life of long-lived, physical assets used in the normal conduct of business and not intended for resale.

+ References

No definition available.

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- Definition

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

+ References

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-Name Accounting Standards Codification

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-SubTopic 10

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Amount before accumulated depreciation of building structures held for productive use including addition, improvement, or renovation to the structure, including, but not limited to, interior masonry, interior flooring, electrical, and plumbing.

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- Definition

Percentage of voting equity interests acquired at the acquisition date in the business combination.

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Amount of structure or a modification to a structure under construction. Includes recently completed structures or modifications to structures that have not been placed into service.

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- Definition

Amount before accumulated depreciation of equipment commonly used in offices and stores that have no permanent connection to the structure of a building or utilities. Examples include, but are not limited to, desks, chairs, tables, and bookcases.

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Amount before accumulated depletion of real estate held for productive use, excluding land held for sale.

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Amount of acquisition of long-lived, physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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