Income Taxes Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Income Tax Disclosure [Abstract]
Income tax expense	$ 50	$ 113	$ 66	$ 162
(Loss) income before income tax expense	$ (235)	$ 654	$ (1,828)	$ 1,125
Effective income tax rate	(21.30%)	17.30%	(3.60%)	14.40%
Statutory federal income tax rate			35.00%