Income Taxes Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Tax Disclosure [Abstract]
Income tax expense	$ 15	$ 22	$ 81	$ 184
(Loss) income before income tax expense	$ 253	$ (918)	$ (1,575)	$ 207
Effective income tax rate	5.90%	(2.40%)	(5.10%)	88.90%
Statutory federal income tax rate	35.00%	35.00%	35.00%	35.00%