Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reconciliation of Unrecognized Tax Benefits
Balance at beginning of period	$ 81	$ 88	$ 82
Increases related to prior year tax positions	10	15	27
Decreases related to prior year tax positions	(10)	(12)	(6)
Settlements	(14)	(6)	(9)
Foreign currency impact	(15)	(4)	(6)
Increases related to current year tax positions	2	0	1
Lapse of statute of limitations	0	0	(1)
Balance at end of period	$ 54	$ 81	$ 88