Unresolved Claims by Claimant (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2008	Dec. 31, 2011 Gse [Member]	Dec. 31, 2011 Private Label [Member]
Loss Contingencies [Line Items]
Balance, beginning of period		$ 150	$ 11
New demands		328	22
Loan paydowns/payoffs		(3)
Resolved claims		(428)	(14)
Balance, end of period		$ 47	$ 19
Balance, beginning of period		845,000,000	71,000,000
New demands	2	2,050,000,000	107,000,000
Loan paydowns/payoffs		(21,000,000)	(2,000,000)
Resolved claims		(2,546,000,000)	(67,000,000)
Balance, end of period		328,000,000	109,000,000