Subsequent Events (Details) (USD $)	1 Months Ended		12 Months Ended
	Jan. 31, 2013	Jun. 30, 2010	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Subsequent Event [Line Items]
Shares of common stock issued			22,700,000
Stock Issued During Period, Value, Other	$ 14.25
Proceeds from issuance of common shares, net	571,900,000	298,100,000	315,295,000	0	298,004,000
Long-term Line of Credit			285,000,000	20,293,000
Cumulative Preferred Stock [Member]
Subsequent Event [Line Items]
Stock Redeemed or Called During Period, Shares	711,820
Preferred Stock, Amount to be Redeemed Subsequent to Period End	178,000,000
Preferred Stock, Redemption Price Per Share	$ 250.00
Common Stock [Member]
Subsequent Event [Line Items]
Shares of common stock issued	41,400,000	26,500,000
Declaration of Dividends [Member] | Common Stock [Member]
Subsequent Event [Line Items]
Common Stock, Dividends, Per Share, Declared			$ 0.170000
Dividends Payable, Date of Record			Feb. 13, 2013
Dividends Payable, Date to be Paid			Feb. 28, 2013
Declaration of Dividends [Member] | 6.625% Series J Preferred Stock [Member]
Subsequent Event [Line Items]
Preferred stock dividends declared per share			$ 0.414063
Dividends Payable, Date of Record			Feb. 13, 2013
Dividends Payable, Date to be Paid			Feb. 28, 2013
Declaration of Dividends [Member] | 6.500% Series K Preferred Stock [Member]
Subsequent Event [Line Items]
Preferred stock dividends declared per share			$ 0.406250
Dividends Payable, Date of Record			Feb. 13, 2013
Dividends Payable, Date to be Paid			Feb. 28, 2013
Declaration of Dividends [Member] | 6.600% Series L Preferred Stock [Member]
Subsequent Event [Line Items]
Preferred stock dividends declared per share			$ 0.412500
Dividends Payable, Date of Record			Feb. 13, 2013
Dividends Payable, Date to be Paid			Feb. 28, 2013
Gross Proceeds [Member]
Subsequent Event [Line Items]
Proceeds from issuance of common shares, net	$ 590,000,000		$ 322,200,000