Subsequent Events (Details Textuals) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended												12 Months Ended			3 Months Ended												12 Months Ended			3 Months Ended
	Dec. 31, 2012 Series A Preferred Stock [Member]	Sep. 30, 2012 Series A Preferred Stock [Member]	Jun. 30, 2012 Series A Preferred Stock [Member]	Mar. 31, 2012 Series A Preferred Stock [Member]	Dec. 31, 2011 Series A Preferred Stock [Member]	Sep. 30, 2011 Series A Preferred Stock [Member]	Jun. 30, 2011 Series A Preferred Stock [Member]	Mar. 31, 2011 Series A Preferred Stock [Member]	Dec. 31, 2010 Series A Preferred Stock [Member]	Sep. 30, 2010 Series A Preferred Stock [Member]	Jun. 30, 2010 Series A Preferred Stock [Member]	Mar. 31, 2010 Series A Preferred Stock [Member]	Dec. 31, 2012 Series A Preferred Stock [Member]	Dec. 31, 2011 Series A Preferred Stock [Member]	Dec. 31, 2010 Series A Preferred Stock [Member]	Dec. 31, 2012 Series B Preferred Stock [Member]	Sep. 30, 2012 Series B Preferred Stock [Member]	Jun. 30, 2012 Series B Preferred Stock [Member]	Mar. 31, 2012 Series B Preferred Stock [Member]	Dec. 31, 2011 Series B Preferred Stock [Member]	Sep. 30, 2011 Series B Preferred Stock [Member]	Jun. 30, 2011 Series B Preferred Stock [Member]	Mar. 31, 2011 Series B Preferred Stock [Member]	Dec. 31, 2010 Series B Preferred Stock [Member]	Sep. 30, 2010 Series B Preferred Stock [Member]	Jun. 30, 2010 Series B Preferred Stock [Member]	Mar. 31, 2010 Series B Preferred Stock [Member]	Dec. 31, 2012 Series B Preferred Stock [Member]	Dec. 31, 2011 Series B Preferred Stock [Member]	Dec. 31, 2010 Series B Preferred Stock [Member]	Mar. 31, 2013 Subsequent Event [Member] Dividends Declared [Member] Series A Preferred Stock [Member]	Mar. 31, 2013 Subsequent Event [Member] Dividends Declared [Member] Series B Preferred Stock [Member]	Mar. 31, 2013 Subsequent Event [Member] Dividends Declared [Member] Common Stock [Member]
Subsequent Event [Line Items]
Preferred stock, dividend rate																															$ 0.250	$ 0.406
Preferred stock, dividends	$ 7	$ 6	$ 7	$ 6	$ 7	$ 6	$ 7	$ 6	$ 7	$ 6	$ 7	$ 6	$ 26	$ 26	$ 26	$ 24	$ 24	$ 24	$ 24	$ 24	$ 24	$ 24	$ 24	$ 24	$ 24	$ 24	$ 24	$ 96	$ 96	$ 96	$ 6	$ 24
Approved annual dividend, amount per share																																	$ 0.185
Estimated aggregate dividend payment																																	$ 203