Income Taxes Accounting for Uncertainty in Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Unrecognized tax benefits balance	$ 34	$ 34	$ 52	$ 56
Addition based on tax positions related to the current year	0	0	2
Increase for tax positions of prior years	6	0	0
Decrease for tax positions of prior years	0	(3)	(1)
Decrease for statute of limitation expiration	$ (6)	$ (15)	$ (5)