Commitments (Unresolved Claims by Claimant) (Detail) $ in Millions	6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)
GSE
Loss Contingencies Dollars
Balance, beginning of period	$ 2	$ 4
New demands	8	10
Loan paydowns/payoffs	0	(1)
Resolved demands	(8)	(9)
Balance, end of period	$ 2	$ 4
Loss Contingencies Units
Balance, beginning of period	13	16
New demands	58	142
Loan paydowns/payoffs	(1)	(6)
Resolved demands	(54)	(134)
Balance, end of period	16	18
Private Label
Loss Contingencies Dollars
Balance, beginning of period	$ 0	$ 0
New demands	0	0
Loan paydowns/payoffs	0	0
Resolved demands	0	0
Balance, end of period	$ 0	$ 0
Loss Contingencies Units
Balance, beginning of period	0	2
New demands	0	3
Loan paydowns/payoffs	0	0
Resolved demands	0	(4)
Balance, end of period	0	1