Fair Value Measurements (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Recurring
Transfers into or out of Level 1 or Level 2 or Level 3	$ 0	$ 0
Total liabilities at fair value	341	699
Nonrecurring
Total liabilities at fair value	$ 0	$ 0