Investments (Schedule of Investments) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Equity And Cost Method Investments [Line Items]
Fair Value Method	$ 597	$ 198
Equity Method	3,546	2,376
Cost Method	2,807	2,770
Total Investments	6,950	5,344
Less: Current investments	19	97
Noncurrent investments	6,931	5,247
Snap [Member]
Fair Value, Equity And Cost Method Investments [Line Items]
Fair Value Method	430	0
Other Fair Value Method Investments [Member]
Fair Value, Equity And Cost Method Investments [Line Items]
Fair Value Method	167	198
Atairos [Member]
Fair Value, Equity And Cost Method Investments [Line Items]
Equity Method	2,388	1,601
Hulu [Member]
Fair Value, Equity And Cost Method Investments [Line Items]
Equity Method	249	225
Other Equity Method Investments [Member]
Fair Value, Equity And Cost Method Investments [Line Items]
Equity Method	909	550
Air Touch [Member]
Fair Value, Equity And Cost Method Investments [Line Items]
Cost Method	1,614	1,599
BuzzFeed [Member]
Fair Value, Equity And Cost Method Investments [Line Items]
Cost Method	400	400
Other Cost Method Investments [Member]
Fair Value, Equity And Cost Method Investments [Line Items]
Cost Method	793	771
NBCUniversal Media LLC [Member]
Fair Value, Equity And Cost Method Investments [Line Items]
Fair Value Method	430	6
Equity Method	690	561
Cost Method	696	696
Noncurrent investments	1,816	1,263
NBCUniversal Media LLC [Member] | Snap [Member]
Fair Value, Equity And Cost Method Investments [Line Items]
Fair Value Method	430	0
NBCUniversal Media LLC [Member] | Other Fair Value Method Investments [Member]
Fair Value, Equity And Cost Method Investments [Line Items]
Fair Value Method	0	6
NBCUniversal Media LLC [Member] | Hulu [Member]
Fair Value, Equity And Cost Method Investments [Line Items]
Equity Method	249	225
NBCUniversal Media LLC [Member] | Other Equity Method Investments [Member]
Fair Value, Equity And Cost Method Investments [Line Items]
Equity Method	441	336
NBCUniversal Media LLC [Member] | BuzzFeed [Member]
Fair Value, Equity And Cost Method Investments [Line Items]
Cost Method	400	400
NBCUniversal Media LLC [Member] | Other Cost Method Investments [Member]
Fair Value, Equity And Cost Method Investments [Line Items]
Cost Method	$ 296	$ 296