Unresolved Claims by Claimant (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended	9 Months Ended
	Dec. 31, 2009	Sep. 30, 2013 GSE number	Sep. 30, 2012 GSE number	Sep. 30, 2013 Private Label number	Sep. 30, 2012 Private Label number
Loss Contingencies Dollars
Balance, beginning of period		$ 48	$ 47	$ 19	$ 19
New demands		189	274	2	6
Loan paydowns/payoffs		2	5	1
Resolved claims		(190)	(261)	(16)	(6)
Balance, end of period		$ 45	$ 55	$ 4	$ 19
Loss Contingencies Units
Balance, beginning of period		294,000,000	328,000,000	124,000,000	109,000,000
New demands	2	1,409,000,000	2,116,000,000	223,000,000	173,000,000
Loan paydowns/payoffs		(11,000,000)	(34,000,000)	(6,000,000)	(1,000,000)
Resolved claims		(1,397,000,000)	(2,092,000,000)	(311,000,000)	(157,000,000)
Balance, end of period		295,000,000	318,000,000	30,000,000	124,000,000