Unresolved Claims by Claimant (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2014 number	Sep. 30, 2013 number
GSE
Loss Contingencies Dollars
Balance, beginning of period	$ 41	$ 48
New demands	84	189
Loan paydowns/payoffs	(4)	(2)
Resolved claims	(106)	(190)
Balance, end of period	15	45
Loss Contingencies Units
Balance, beginning of period	264,000,000	294,000,000
New demands	643,000,000	1,409,000,000
Loan paydowns/payoffs	(33,000,000)	(11,000,000)
Resolved claims	(780,000,000)	(1,397,000,000)
Balance, end of period	94,000,000	295,000,000
Private Label
Loss Contingencies Dollars
Balance, beginning of period	5	19
New demands		2
Loan paydowns/payoffs	(1)	(1)
Resolved claims	(4)	(16)
Balance, end of period		$ 4
Loss Contingencies Units
Balance, beginning of period	33,000,000	124,000,000
New demands	11,000,000	223,000,000
Loan paydowns/payoffs	(2,000,000)	(6,000,000)
Resolved claims	(42,000,000)	(311,000,000)
Balance, end of period		30,000,000