Subsequent Events (Details) (Declaration of Dividends [Member], USD $)	3 Months Ended
	Mar. 31, 2012
Subsequent Event [Line Items]
Declared date	Apr. 25, 2012
Common Stock [Member]
Subsequent Event [Line Items]
Common stock dividends declared per share	0.17
Record date	May 16, 2012
Payment date	May 31, 2012
Series J Preferred Stock [Member]
Subsequent Event [Line Items]
Preferred stock dividends declared per share	0.414063
Record date	May 16, 2012
Payment date	May 31, 2012
Series K Preferred Stock [Member]
Subsequent Event [Line Items]
Preferred stock dividends declared per share	0.406250
Record date	May 16, 2012
Payment date	May 31, 2012
Series L Preferred Stock [Member]
Subsequent Event [Line Items]
Preferred stock dividends declared per share	0.412500
Record date	May 16, 2012
Payment date	May 31, 2012
Series O Preferred Stock [Member]
Subsequent Event [Line Items]
Preferred stock dividends declared per share	0.523437
Record date	Jun. 15, 2012
Payment date	Jul. 02, 2012