Expected Losses to be Paid (Components of Development and Accretion Amounts of Estimated Recoveries) (Details 8) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Expected Losses [Abstract]
Inclusion of new deals with breaches of R&W during period	$ (3)	$ 115
Change in recovery assumptions as the result of additional file review and recovery success	70	218
Estimated increase (decrease) in defaults that will result in additional breaches	63	17
Results of settlements	40	668
Accretion of discount on balance	9	20
Expected Future Recoveries for Breached Representations and Warranties Development and Accretion of Discount	$ 179	$ 1,038