Unresolved Claims by Claimant (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014 number	Mar. 31, 2013 number
GSE
Loss Contingencies Dollars
Balance, beginning of period	$ 41	$ 48
New demands	34	66
Loan paydowns/payoffs	(1)	(1)
Resolved claims	(55)	(71)
Balance, end of period	19	42
Loss Contingencies Units
Balance, beginning of period	264,000,000	294,000,000
New demands	230,000,000	458,000,000
Loan paydowns/payoffs	(16,000,000)	(5,000,000)
Resolved claims	(375,000,000)	(484,000,000)
Balance, end of period	103,000,000	263,000,000
Private Label
Loss Contingencies Dollars
Balance, beginning of period	5	19
New demands	1	1
Loan paydowns/payoffs	(1)	(1)
Resolved claims	(3)	(14)
Balance, end of period	$ 2	$ 5
Loss Contingencies Units
Balance, beginning of period	33,000,000	124,000,000
New demands	10,000,000	76,000,000
Loan paydowns/payoffs	(2,000,000)	(4,000,000)
Resolved claims	(31,000,000)	(163,000,000)
Balance, end of period	10,000,000	33,000,000