Derivative Instruments - Additional Information (Detail) (USD $)		3 Months Ended
	Mar. 31, 2013	Mar. 31, 2013 Put Option [Member]	Mar. 31, 2013 Interest rate swaps [Member]	Mar. 31, 2012 Interest rate swaps [Member]	Feb. 13, 2013 Derivatives designated as hedging instruments [Member] Interest rate caps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Number of interest rate swap agreements			8
Notional amount of interest rate swap agreements			$ 5,750,000,000		$ 4,664,100,000
LIBOR cap rate					4.50%
Increase (decrease) in interest expense			42,200,000	41,800,000
Aggregate cash payment		17,500,000
Aggregate cash payment, fair value		0
Interest rate swap agreements, represents total debt	19.00%
Fixed-rate debt represents total debt	81.00%
Excluding variable rate debt	$ 5,750,000,000