Unresolved Claims by Claimant (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended	3 Months Ended
	Dec. 31, 2009	Mar. 31, 2012 Gse [Member] number	Mar. 31, 2012 Private Label [Member] number
Loss Contingencies [Line Items]
Balance, beginning of period		$ 47	$ 19
New demands		93	1
Loan paydowns/payoffs		(2)
Resolved claims		(78)	(2)
Balance, end of period		$ 60	$ 18
Balance, beginning of period		328,000,000	109,000,000
New demands	2	773,000,000	61,000,000
Loan paydowns/payoffs		(15,000,000)
Resolved claims		(672,000,000)	(58,000,000)
Balance, end of period		414,000,000	112,000,000