Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Jan. 01, 2016
Income Tax Disclosure [Abstract]
Tax expense	$ 78	$ 123
Income before income taxes	267	359
(Favorable) unfavorable impact on income tax expense, certain items	(12)
(Favorable) unfavorable impact on income tax expense, release of valuation allowance	(7)
(Favorable) unfavorable impact on income tax expense, discrete tax adjustments	(5)	$ 4
Possible valuation allowance reduction	$ 275
Unrecognized tax benefits			$ 54
Favorable impact of unrecognized tax benefits if recognized			40
Accrued interest			5
Unsettled unrecognized tax benefits that would require cash			$ 9