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Investments (Equity Method) (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Feb. 28, 2018	Jan. 31, 2018	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Equity method investments		$ 4,007		$ 4,007				$ 3,546
Equity in net income (losses) of investees, net		69	$ 15	20	$ 51
NBCUniversal Media LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments		719		719				690
Equity in net income (losses) of investees, net		(87)	(29)	(187)	(55)
Atairos [Member]
Schedule of Equity Method Investments [Line Items]
Funding commitment						$ 5,000	$ 4,000
Equity method investments		2,700		2,700				2,400
Purchases of investments				112	994
Equity in net income (losses) of investees, net		151	42	186	99
Pretax gain, sale of business to Atairos		200		200
Hulu [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments		238		238				249
Cash contributions to equity method investments				227	99
Equity in net income (losses) of investees, net		(107)	(52)	(238)	(106)
Hulu [Member] | NBCUniversal Media LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments		238		238				$ 249
Cash contributions to equity method investments				227	99
Equity in net income (losses) of investees, net		$ (107)	$ (52)	$ (238)	$ (106)
The Weather Channel [Member]
Schedule of Equity Method Investments [Line Items]
Pretax gain on sale of investment	$ 64
The Weather Channel [Member] | NBCUniversal Media LLC [Member]
Schedule of Equity Method Investments [Line Items]
Pretax gain on sale of investment	$ 64

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