Derivative Instruments (Details Textual) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012 Contract	Jun. 30, 2011	Jun. 30, 2012 Contract	Jun. 30, 2011	Jan. 18, 2012
Derivative instruments (Textual) [Abstract]
Number of interest rate swap contracts					3
Cash flow hedging instruments	$ 4,650.2		$ 4,650.2
Increase (decrease) in interest expense	5.2		10.4
Aggregate principal amount of senior secured notes	22,707.4		22,707.4
Derivative Instruments (Additional Textual) [Abstract]
LIBOR and fixed payment rate					0.165%
LIBOR cap rate	4.50%		4.50%
Increase (decrease) in interest expense	5.2		10.4
Additional increase (decrease) to interest expense			13.9
Excluding variable rate debt	5,750.0		5,750.0
Interest rate swap agreements, represents total debt	28.00%		28.00%
Fixed-rate debt represents total debt	72.00%		72.00%
Put Option [Member]
Derivative instruments (Textual) [Abstract]
Notional amount of interest rate swap agreements	33.2		33.2
Aggregate cash payment	33.2
Derivative Option at fair value	0		0
CMBS [Member]
Derivative instruments (Textual) [Abstract]
Interest rate cap agreement termination date			Feb. 13, 2013
Credit Facility Term Loan [Member]
Derivative instruments (Textual) [Abstract]
Aggregate principal amount of senior secured notes					3,000.0
Interest Rate Swap [Member]
Derivative instruments (Textual) [Abstract]
No of interest rate swap agreements	8		8
Notional amount of interest rate swap agreements	5,750.0		5,750.0		1,000.0
Increase (decrease) in interest expense	42.2	84.0	50.8	117.3
Derivative Instruments (Additional Textual) [Abstract]
Increase (decrease) in interest expense	42.2	84.0	50.8	117.3
Interest Rate Cap [Member]
Derivative instruments (Textual) [Abstract]
Notional amount of interest rate swap agreements	$ 6,500.0		$ 6,500.0