Investments in Unconsolidated Entities - Schedule of Investments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Equity Method Investments and Joint Ventures [Abstract]
Equity method investments	$ 443		$ 443		$ 434
Measurement alternative method investments	7		7		7
Total investments in unconsolidated entities	450		450		$ 441
Equity method investments, combined income statements
Revenues	1,654	$ 1,655	3,343	$ 3,312
Operating expenses	1,187	1,199	2,402	2,407
Operating income	467	456	941	905
Other income (expense), net	4	2	(2)	1
Net income	$ 471	$ 458	$ 939	$ 906