Income Taxes Income Taxes (Schedule of Unrecognized Tax Benefits Roll Forward) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Unrecognized Tax Benefits	$ 14	$ 185	$ 191
Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions	0	0	0
Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions	3	12	7
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions	(1)	0	0
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities	0	(182)	(10)
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	(1)	(1)	(3)
Unrecognized Tax Benefits	$ 15	$ 14	$ 185