Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Jan. 01, 2017
Income Tax Disclosure [Abstract]
Tax expense	$ 30	$ (10)	$ 136	$ 161
Income before income taxes	162	310	591	878
Favorable impact on income tax expense, discrete tax adjustments	$ 12	$ 118	$ 23	$ 127
Unrecognized tax benefits					$ 63
Favorable impact on income tax expense, if unrecognized tax benefits were recognized					47
Accrued interest					4
Unrecognized tax benefits requiring the use of cash if not favorably settled					$ 12