Summary of Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Required Annual Distribution of Taxable Net Income	90.00%
Unrealized (loss) gain on derivative instruments, net	$ 49	$ 52
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