Summary of Significant Accounting Policies - Foreign Currency (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accounting Policies [Abstract]
Cumulative translation loss, net of tax	$ (430)	$ (227)
Foreign currency exchange losses, net	$ (66)	$ (87)	$ (14)