Commitments (Unresolved Claims by Claimant) (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
GSE
Loss Contingencies Dollars
Balance, beginning of period	$ 4	$ 6
New demands	22	33
Loan paydowns/payoffs	(1)	(2)
Resolved claims	(23)	(33)
Balance, end of period	$ 2	$ 4
Loss Contingencies Units
Balance, beginning of period	16	37
New demands	309	436
Loan paydowns/payoffs	(8)	(29)
Resolved claims	(304)	(428)
Balance, end of period	13	16
Private Label
Loss Contingencies Dollars
Balance, beginning of period	$ 0	$ 1
New demands	0	42
Loan paydowns/payoffs	0	0
Resolved claims	0	(43)
Balance, end of period	$ 0	$ 0
Loss Contingencies Units
Balance, beginning of period	2	1
New demands	4	261
Loan paydowns/payoffs	0	0
Resolved claims	(6)	(260)
Balance, end of period	0	2