Commitments - Unresolved Claims by Claimant (Details) $ in Millions	9 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)
GSE
Loss Contingencies Dollars
Balance, beginning of period	$ 1	$ 1
New demands	38	17
Loan paydowns/payoffs	0
Resolved demands	34	13
Balance, end of period	$ 5	$ 5
Loss Contingencies Units
Balance, beginning of period	9	6
New demands	213	104
Loan paydowns/payoffs	(3)
Resolved demands	(194)	(85)
Balance, end of period	25	25
Private Label
Loss Contingencies Dollars
Balance, beginning of period	$ 0	$ 0
New demands	0	0
Loan paydowns/payoffs	0
Resolved demands	0	0
Balance, end of period	$ 0	$ 0
Loss Contingencies Units
Balance, beginning of period	1	1
New demands	7	0
Loan paydowns/payoffs	0
Resolved demands	(3)	0
Balance, end of period	5	1