Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Jan. 01, 2016
Income Tax Disclosure [Abstract]
Tax expense (benefit)	$ (10)	$ 126	$ 161	$ 369
Income before income taxes	310	431	878	$ 1,118
Favorable impact to income tax expense	118		127
Favorable impact on income taxes, foreign taxes credit election	163
(Favorable) unfavorable impact on income tax expense, change in valuation allowance	41		(7)
(Favorable) unfavorable impact on income tax expense, foreign tax settlements	7	$ (8)
Possible valuation allowance reduction	$ 340		$ 340
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