Income Taxes (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	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
Dividends Payable [Line Items]
Undistributed Taxable Income									$ 749
Preferred Stock Dividends, Shares									$ 1.056
Common Stock, Dividends, Per Share, Declared	$ 1.25	$ 1.25	$ 1.25	$ 1.25	$ 1.40	$ 1.40	$ 1.40	$ 1.40	$ 5.00	$ 5.60	$ 5.60
Dividends, Common Stock, Cash									(1,518)	(886)	(230)
Excise and Sales Taxes									25	2
Ordinary Income [Member]
Dividends Payable [Line Items]
Preferred Stock Dividends, Shares									$ 0.9523
Common Stock, Dividends, Per Share, Declared									$ 4.5092	$ 5.3324	$ 4.9314
Long-term Capital Gains [Member]
Dividends Payable [Line Items]
Preferred Stock Dividends, Shares									$ 0.1037
Common Stock, Dividends, Per Share, Declared									$ 0.4908	$ 0.2676	$ 0.6686
Taxable REIT Subsidiary [Member]
Dividends Payable [Line Items]
Current Income Tax Expense (Benefit)									(6)	4
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate									39.50%
Preferred Stock [Member]
Dividends Payable [Line Items]
Dividends, Preferred Stock, Cash									7
Common Stock [Member]
Dividends Payable [Line Items]
Dividends, Common Stock, Cash									$ 1,518	$ 886	$ 230