Unresolved Claims by Claimant (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
GSE
Loss Contingencies Dollars
Balance, beginning of period	$ 41	$ 48
New demands	95	259
Loan paydowns/payoffs	(5)	(3)
Resolved claims	(125)	(263)
Balance, end of period	6	41
Loss Contingencies Units
Balance, beginning of period	264,000,000	294,000,000
New demands	744,000,000	1,962,000,000
Loan paydowns/payoffs	(44,000,000)	(20,000,000)
Resolved claims	(927,000,000)	(1,972,000,000)
Balance, end of period	37,000,000	264,000,000
Private Label
Loss Contingencies Dollars
Balance, beginning of period	5	19
New demands	2	4
Loan paydowns/payoffs	(1)	(1)
Resolved claims	(5)	(17)
Balance, end of period	$ 1	$ 5
Loss Contingencies Units
Balance, beginning of period	33,000,000	124,000,000
New demands	14,000,000	237,000,000
Loan paydowns/payoffs	(2,000,000)	(6,000,000)
Resolved claims	(44,000,000)	(322,000,000)
Balance, end of period	1,000,000	33,000,000