Income Taxes Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Income Tax Disclosure [Abstract]
Income tax expense	$ 113	$ 82	$ 162	$ 185
Income before income tax expense	$ 654	$ 1,205	$ 1,125	$ 1,385
Effective income tax rate	17.30%	6.80%	14.40%	13.40%
Statutory federal income tax rate	35.00%		35.00%