Accumulated Other Comprehensive Income (Details) - USD ($)	3 Months Ended				9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2014	Sep. 30, 2012	Sep. 30, 2018	Sep. 30, 2017
Cumulative Translation Adjustment Summary [Roll Forward]
Beginning balance	$ (670,000,000)	$ (609,000,000)			$ (419,000,000)	$ (890,000,000)
Net gain/(loss) on Foreign Currency Transaction	(49,000,000)	204,000,000			(300,000,000)	485,000,000
Ending balance	$ (719,000,000)	$ (405,000,000)			(719,000,000)	(405,000,000)
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax [Abstract]
Net gain/(loss) on foreign currency translation, tax adjustment			$ 0	$ 0	$ 0	$ 0