Unresolved Claims by Claimant (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended	9 Months Ended
	Dec. 31, 2008	Sep. 30, 2011 Gse [Member]	Sep. 30, 2011 Private Label [Member]
Loss Contingencies [Line Items]
Balance, beginning of period		$ 150	$ 11
New demands		259	22
Loan paydowns/payoffs		(3)
Resolved claims		(342)	(12)
Balance, end of period		$ 64	$ 21
Balance, beginning of period		845,000,000	71,000,000
New demands	2	1,550,000,000	93,000,000
Loan paydowns/payoffs		(17,000,000)	(2,000,000)
Resolved claims		(1,977,000,000)	(62,000,000)
Balance, end of period		401,000,000	100,000,000