Investments in Unconsolidated Entities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Equity method investments, combined income statements
Revenues	$ 1,682	$ 1,730
Operating expenses	1,230	1,287
Operating income	452	443
Other income (expense), net	(4)	5
Net income	$ 448	$ 448