Income Taxes (Income Tax Contingencies) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Balance, beginning of period	$ (38)	$ (59)	$ (58)
Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions	7	0	0
Decreases related to prior year tax positions	17	11	1
Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions	0	(2)	(2)
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	0	12	0
Balance, end of period	$ (28)	$ (38)	$ (59)