Financial Instruments (Offsetting Assets) (Details) - Prepaid expenses and other current assets - USD ($) $ in Millions	Dec. 31, 2014	Dec. 31, 2013
Offsetting Assets [Line Items]
Gross assets	$ 31	$ 13
Gross assets offset in Balance Sheet	0	0
Net recognized assets in Balance Sheet	31	13
Financial Instruments	(3)	(2)
Cash Collateral	0	0
Net Amount	28	11
Gasoline swaps
Offsetting Assets [Line Items]
Gross assets		2
Gross assets offset in Balance Sheet		0
Net recognized assets in Balance Sheet		2
Financial Instruments		0
Cash Collateral		0
Net Amount		2
Interest rate caps
Offsetting Assets [Line Items]
Gross assets	25	9
Gross assets offset in Balance Sheet	0	0
Net recognized assets in Balance Sheet	25	9
Financial Instruments	0	0
Cash Collateral	0	0
Net Amount	25	9
Foreign exchange forward contracts
Offsetting Assets [Line Items]
Gross assets	6	2
Gross assets offset in Balance Sheet	0	0
Net recognized assets in Balance Sheet	6	2
Financial Instruments	(3)	(2)
Cash Collateral	0	0
Net Amount	$ 3	$ 0