Subsequent Events (Details) (Declaration of Dividends [Member], USD $)	3 Months Ended	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2012
Subsequent Event [Line Items]
Declared date		Jul. 25, 2012
Common Stock [Member]
Subsequent Event [Line Items]
Common stock dividends declared per share	$ 0.17
Record date		Aug. 15, 2012
Payment date		Aug. 31, 2012
Series J Preferred Stock [Member]
Subsequent Event [Line Items]
Preferred stock dividends declared per share	$ 0.414063
Record date		Aug. 15, 2012
Payment date		Aug. 31, 2012
Series K Preferred Stock [Member]
Subsequent Event [Line Items]
Preferred stock dividends declared per share	$ 0.406250
Record date		Aug. 15, 2012
Payment date		Aug. 31, 2012
Series L Preferred Stock [Member]
Subsequent Event [Line Items]
Preferred stock dividends declared per share	$ 0.412500
Record date		Aug. 15, 2012
Payment date		Aug. 31, 2012
Series O Preferred Stock [Member]
Subsequent Event [Line Items]
Preferred stock dividends declared per share	$ 0.523437
Record date		Sep. 17, 2012
Payment date		Oct. 01, 2012