Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reconciliation of Unrecognized Tax Benefits
Balance at beginning of period	$ 54	$ 81	$ 88
Increases related to prior year tax positions	19	10	15
Decreases related to prior year tax positions	(8)	(10)	(12)
Settlements	(8)	(14)	(6)
Foreign currency impact	6	(15)	(4)
Increases related to current year tax positions	1	2	0
Lapse of statute of limitations	(1)	0	0
Balance at end of period	$ 63	$ 54	$ 81