Income Taxes Uncertain Tax Positions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits Excluding Amounts Pertaining to Examined Tax Returns RollForward [Abstract]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	$ 34
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning Balance	62	$ 69	$ 78
Additions for tax positions related to current year	7	4	7
Reductions for tax positions taken in prior years	(1)	(1)	(8)
Additions for tax positions as a result of settlements	0	1	1
Reductions for tax positions as a result of lapse of statute of limitations	(11)	(11)	(9)
Ending Balance	57	62	69
Total accrued liabilities for interest and penalites	6	$ 5
Total interest and penalties recognized as expense (benefit)	$ 1		$ (4)