Investment in Unconsolidated Entities - Schedule of Investments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Equity Method Investments and Joint Ventures [Abstract]
Equity method investments	$ 485		$ 459
Measurement alternative method investments	22		21
Total investments in unconsolidated entities	507	$ 488	$ 480
Equity method investments, combined income statements
Revenues	1,696	1,663
Operating expenses	1,221	1,213
Operating income	475	450
Other income (expense), net	(6)	(1)
Net income	$ 469	$ 449