Commitments and Contingencies (Details) (Pending Litigation [Member], USD $) In Billions, unless otherwise specified	1 Months Ended
	May 31, 2008	Dec. 31, 2007
Series T Preferred Stock [Member] | Comprehensive Investment Services v. Mudd, et al. [Member]
Loss Contingencies [Line Items]
Preferred stock offering amount	$ 2.0
Preferred stock, annual dividend rate	8.25%
Series S Preferred Stock [Member] | Smith v. Fannie Mae, et al. [Member]
Loss Contingencies [Line Items]
Preferred stock offering amount		$ 7.0
Preferred stock, annual dividend rate		7.75%