Income Taxes Valuation Allowance Rollforward (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Valuation allowance, beginning of period	$ (35)	$ (82)	$ (91)
Additions related to tax reform (reduced federal benefit)	(4)	0	0
Reductions related to the wind-down of foreign operations	14	0	14
Reductions (additions) related to state valuation allowance release	2	47	(5)
Valuation allowance, end of period	$ (23)	$ (35)	$ (82)