Financial Instruments (Details) - Fair Value, Measurements, Recurring - Not Designated as Hedging Instrument - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset Derivatives	$ 12		$ 12		$ 31
Liability Derivatives	10		10		27
Interest Rate Cap | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset Derivatives	8		8		25
Liability Derivatives	8		8		25
Foreign Exchange Forward
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign currency forward contracts	(3)	$ 5	(4)	$ 0
Foreign Exchange Forward | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset Derivatives	4		4		6
Liability Derivatives	$ 2		$ 2		$ 2