Investments in Unconsolidated Entities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Equity and measurement alternative method investments
Equity method investments	$ 444		$ 411
Measurement alternative method investments	6		4
Total investments in unconsolidated entities	450		$ 415
Equity method investments, combined income statements
Revenues	1,657	$ 1,610
Operating expenses	1,208	1,212
Operating income	449	398
Other expense, net	(1)
Net income	$ 448	$ 398