Summary of Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended							12 Months Ended
	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
REIT Capital Gain Distribution %								95.00%
Required Annual Distribution of Taxable Net Income								90.00%
REIT Ordinary Income Distribution %								85.00%
Unrealized (loss) gain on derivative instruments, net	$ 51	$ 52	$ 52	$ 54	$ (513)	$ (252)	$ 61	$ 205	$ (650)	$ (24)
Excise Tax Rate								4.00%
One Month [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Interest Rate Derivative Not Designated As Hedging Instruments Average receive Rate								100.00%
Three Month [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Interest Rate Derivative Not Designated As Hedging Instruments Average receive Rate								300.00%
Maximum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Interest Rate Derivative Not Designated As Hedging Instruments Average receive Rate								600.00%
Interest Rate Swap [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Derivative, Average Remaining Maturity								10 years