Unresolved Claims by Claimant (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015 number	Mar. 31, 2014 number
GSE
Loss Contingencies Dollars
Balance, beginning of period	$ 6	$ 41
New demands	9	34
Loan paydowns/payoffs		(1)
Resolved claims	(11)	(55)
Balance, end of period	4	19
Loss Contingencies Units
Balance, beginning of period	37,000,000	264,000,000
New demands	118,000,000	230,000,000
Loan paydowns/payoffs	(4,000,000)	(16,000,000)
Resolved claims	(119,000,000)	(375,000,000)
Balance, end of period	32,000,000	103,000,000
Private Label
Loss Contingencies Dollars
Balance, beginning of period	1	5
New demands		1
Loan paydowns/payoffs		(1)
Resolved claims	(1)	(3)
Balance, end of period		$ 2
Loss Contingencies Units
Balance, beginning of period	1,000,000	33,000,000
New demands	6,000,000	10,000,000
Loan paydowns/payoffs		(2,000,000)
Resolved claims	(5,000,000)	(31,000,000)
Balance, end of period	2,000,000	10,000,000