Income Taxes Income Taxes (Narrative - Unrecognized Tax Benefits) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	$ 177	$ 12	$ 9
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	2	1	$ 1
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense	$ 1
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit		$ 15