Financial Instruments (Details) (USD $)	12 Months Ended					9 Months Ended	12 Months Ended		9 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Level 2	Dec. 31, 2011 Level 2	Sep. 30, 2011 Recurring Derivatives not designated as hedging instruments	Dec. 31, 2012 Recurring Derivatives not designated as hedging instruments	Dec. 31, 2011 Recurring Derivatives not designated as hedging instruments	Sep. 30, 2011 Recurring Derivatives not designated as hedging instruments Interest rate caps	Dec. 31, 2012 Recurring Derivatives not designated as hedging instruments Interest rate caps	Sep. 30, 2011 Recurring Derivatives not designated as hedging instruments Foreign exchange forward contracts	Dec. 31, 2012 Recurring Derivatives not designated as hedging instruments Foreign exchange forward contracts	Sep. 30, 2011 Recurring Derivatives not designated as hedging instruments Foreign exchange options	Dec. 31, 2012 Recurring Derivatives not designated as hedging instruments Foreign exchange options	Sep. 30, 2011 Recurring Derivatives not designated as hedging instruments Gasoline swaps	Dec. 31, 2012 Recurring Derivatives not designated as hedging instruments Gasoline swaps	Dec. 31, 2012 Recurring Level 1 Derivatives not designated as hedging instruments	Dec. 31, 2011 Recurring Level 1 Derivatives not designated as hedging instruments	Dec. 31, 2012 Recurring Level 1 Derivatives not designated as hedging instruments Interest rate caps	Dec. 31, 2011 Recurring Level 1 Derivatives not designated as hedging instruments Interest rate caps	Dec. 31, 2012 Recurring Level 1 Derivatives not designated as hedging instruments Foreign exchange forward contracts	Dec. 31, 2011 Recurring Level 1 Derivatives not designated as hedging instruments Foreign exchange forward contracts	Dec. 31, 2012 Recurring Level 1 Derivatives not designated as hedging instruments Foreign exchange options	Dec. 31, 2011 Recurring Level 1 Derivatives not designated as hedging instruments Foreign exchange options	Dec. 31, 2012 Recurring Level 1 Derivatives not designated as hedging instruments Gasoline swaps	Dec. 31, 2011 Recurring Level 1 Derivatives not designated as hedging instruments Gasoline swaps	Dec. 31, 2012 Recurring Level 2	Dec. 31, 2011 Recurring Level 2	Dec. 31, 2012 Recurring Level 2 Derivatives not designated as hedging instruments		Dec. 31, 2011 Recurring Level 2 Derivatives not designated as hedging instruments		Dec. 31, 2012 Recurring Level 2 Derivatives not designated as hedging instruments Interest rate caps		Dec. 31, 2011 Recurring Level 2 Derivatives not designated as hedging instruments Interest rate caps		Dec. 31, 2012 Recurring Level 2 Derivatives not designated as hedging instruments Foreign exchange forward contracts		Dec. 31, 2011 Recurring Level 2 Derivatives not designated as hedging instruments Foreign exchange forward contracts		Dec. 31, 2012 Recurring Level 2 Derivatives not designated as hedging instruments Foreign exchange options		Dec. 31, 2011 Recurring Level 2 Derivatives not designated as hedging instruments Foreign exchange options		Dec. 31, 2012 Recurring Level 2 Derivatives not designated as hedging instruments Gasoline swaps		Dec. 31, 2011 Recurring Level 2 Derivatives not designated as hedging instruments Gasoline swaps		Dec. 31, 2012 Recurring Level 2 Derivatives not designated as hedging instruments Interest rate swaps		Dec. 31, 2011 Recurring Level 2 Derivatives not designated as hedging instruments Interest rate swaps		Dec. 31, 2012 Recurring Level 3 Derivatives not designated as hedging instruments	Dec. 31, 2011 Recurring Level 3 Derivatives not designated as hedging instruments	Dec. 31, 2012 Recurring Level 3 Derivatives not designated as hedging instruments Interest rate caps	Dec. 31, 2011 Recurring Level 3 Derivatives not designated as hedging instruments Interest rate caps	Dec. 31, 2012 Recurring Level 3 Derivatives not designated as hedging instruments Foreign exchange forward contracts	Dec. 31, 2011 Recurring Level 3 Derivatives not designated as hedging instruments Foreign exchange forward contracts	Dec. 31, 2012 Recurring Level 3 Derivatives not designated as hedging instruments Foreign exchange options	Dec. 31, 2011 Recurring Level 3 Derivatives not designated as hedging instruments Foreign exchange options	Dec. 31, 2012 Recurring Level 3 Derivatives not designated as hedging instruments Gasoline swaps	Dec. 31, 2011 Recurring Level 3 Derivatives not designated as hedging instruments Gasoline swaps	Dec. 31, 2012 Recurring Total Derivatives not designated as hedging instruments	Dec. 31, 2011 Recurring Total Derivatives not designated as hedging instruments	Dec. 31, 2012 Recurring Total Derivatives not designated as hedging instruments Interest rate caps	Dec. 31, 2011 Recurring Total Derivatives not designated as hedging instruments Interest rate caps	Dec. 31, 2012 Recurring Total Derivatives not designated as hedging instruments Foreign exchange forward contracts	Dec. 31, 2011 Recurring Total Derivatives not designated as hedging instruments Foreign exchange forward contracts	Dec. 31, 2012 Recurring Total Derivatives not designated as hedging instruments Foreign exchange options	Dec. 31, 2011 Recurring Total Derivatives not designated as hedging instruments Foreign exchange options	Dec. 31, 2012 Recurring Total Derivatives not designated as hedging instruments Gasoline swaps	Dec. 31, 2011 Recurring Total Derivatives not designated as hedging instruments Gasoline swaps	Dec. 31, 2011 Recurring Total Derivatives not designated as hedging instruments Interest rate swaps
Fair Value of Derivative Instruments
Asset Derivatives																	$ 0	$ 33,200,000	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0					$ 4,500,000	[1],[2]	$ 5,000,000	[1],[2]	$ 900,000	[1],[2]	$ 500,000	[1],[2]	$ 3,400,000	[1],[2]	$ 4,400,000	[1],[2]	$ 200,000	[1],[2]	$ 100,000	[1],[2]	$ 0	[1],[2]	$ 0	[1],[2]	$ 0	[1],[2]	$ 0	[1],[2]	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0			$ 4,500,000	$ 38,200,000	$ 900,000	$ 500,000	$ 3,400,000	$ 4,400,000	$ 200,000	$ 100,000
Liability Derivatives								2,900,000									0	0	0	0	0	0			0	0			5,500,000	[1],[2]	2,900,000	[1],[2]	900,000	[1],[2]	400,000	[1],[2]	4,500,000	[1],[2]	1,900,000	[1],[2]	0	[1],[2]	0	[1],[2]	100,000	[1],[2]	400,000	[1],[2]	0	[1],[2]	200,000	[1],[2]	0	0	0	0	0	0			0	0	5,500,000		900,000	400,000	4,500,000	1,900,000			100,000	400,000	200,000
Amount of Gain or (Loss) Recognized in Income on Derivative	8,470,000	0	0			(8,600,000)	(15,500,000)		0	(800,000)	(11,000,000)	(15,400,000)	(200,000)	0	2,600,000	700,000
Marketable Securities
Investments																		33,200,000													0																							0										33,200,000
Debt
Maximum initial maturity period of borrowings	90 days
Aggregate fair value of all debt				16,493,100,000	11,832,500,000
Aggregate carrying value of all debt																											$ 15,473,800,000	$ 11,400,300,000

[1] All fair value measurements were primarily based upon significant observable (Level 2) inputs.

[2] All asset derivatives are recorded in "Prepaid expenses and other assets" and all liability derivatives are recorded in "Other accrued liabilities" on our consolidated balance sheets.