Commitments (Unresolved Claims by Claimant) (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)
GSE
Loss Contingencies Dollars
Balance, beginning of period	$ 4	$ 6
New demands	18	26
Loan paydowns/payoffs	(1)	(2)
Resolved demands	(14)	(26)
Balance, end of period	$ 7	$ 4
Loss Contingencies Units
Balance, beginning of period	16	37
New demands	253	350
Loan paydowns/payoffs	(8)	(26)
Resolved demands	(203)	(337)
Balance, end of period	58	24
Private Label
Loss Contingencies Dollars
Balance, beginning of period	$ 0	$ 1
New demands	0	42
Loan paydowns/payoffs	0	0
Resolved demands	0	(43)
Balance, end of period	$ 0	$ 0
Loss Contingencies Units
Balance, beginning of period	2	1
New demands	4	257
Loan paydowns/payoffs	0	0
Resolved demands	(6)	(258)
Balance, end of period	0	0