Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Jan. 01, 2017
Income Tax Disclosure [Abstract]
Tax expense	$ 36	$ 93	$ 106	$ 171
Income before income taxes	190	301	429	568
Unfavorable (favorable) impact on income tax expense, discrete tax adjustments	$ (9)	$ 3	$ (11)	$ (9)
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