Property and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	$ 88,386	$ 85,947
Less: Accumulated depreciation	49,916	49,694
Property and equipment, net	38,470	36,253
NBCUniversal Media LLC [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	15,512	13,861
Less: Accumulated depreciation	4,166	3,350
Property and equipment, net	$ 11,346	10,511
Cable Distribution System [Member]
Property, Plant and Equipment [Line Items]
Weighted-Average Original Useful Life	11 years
Property and equipment, at cost	$ 36,046	34,028
Customer Premise Equipment [Member]
Property, Plant and Equipment [Line Items]
Weighted-Average Original Useful Life	6 years
Property and equipment, at cost	$ 26,392	28,621
Other Equipment [Member]
Property, Plant and Equipment [Line Items]
Weighted-Average Original Useful Life	9 years
Property and equipment, at cost	$ 10,518	9,471
Building and Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Weighted-Average Original Useful Life	30 years
Property and equipment, at cost	$ 12,346	10,653
Building and Leasehold Improvements [Member] | NBCUniversal Media LLC [Member]
Property, Plant and Equipment [Line Items]
Weighted-Average Original Useful Life	31 years
Property and equipment, at cost	$ 8,124	7,543
Furniture, Fixtures and Equipment [Member] | NBCUniversal Media LLC [Member]
Property, Plant and Equipment [Line Items]
Weighted-Average Original Useful Life	11 years
Property and equipment, at cost	$ 4,843	4,158
Construction in Process [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	1,752	1,901
Construction in Process [Member] | NBCUniversal Media LLC [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	1,506	1,176
Land [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	1,332	1,273
Land [Member] | NBCUniversal Media LLC [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	$ 1,039	$ 984