Income Taxes Income Tax Expense (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Income tax (benefit) expense	$ (15)	$ 31	$ (20)	$ 78
US Tax Reform, Provisional Tax Expense, Reduction			$ 40