Income Taxes Changes in Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Changes in Unrecognized Tax Benefits [Line Items]
Unrecognized Tax Benefits	$ 141	$ 111	$ 100
Federal and State [Member]
Changes in Unrecognized Tax Benefits [Line Items]
Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions	22	18
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions	(5)	(4)
Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions	13	13
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities	$ 0	$ (16)