Loans Held-for-Investment - Summary of Newly Modified TDRs (Details) $ in Millions	12 Months Ended
Dec. 31, 2019 USD ($) loan	Dec. 31, 2018 USD ($) loan	Dec. 31, 2017 USD ($) loan
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Accounts \| loan	14	31	98
Pre-Modification Unpaid Principal Balance	$ 1	$ 4	$ 10
Post-Modification Unpaid Principal Balance	1	4	9
Increase (Decrease) in Allowance at Modification	$ 0	$ 0	$ (1)
Residential first mortgage
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Accounts \| loan		14	16
Pre-Modification Unpaid Principal Balance		$ 3	$ 4
Post-Modification Unpaid Principal Balance		3	4
Increase (Decrease) in Allowance at Modification		$ 0	$ 0
Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Accounts \| loan		17	82
Pre-Modification Unpaid Principal Balance		$ 1	$ 6
Post-Modification Unpaid Principal Balance		1	5
Increase (Decrease) in Allowance at Modification		$ 0	$ (1)
Other consumer \| Residential first mortgage
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Accounts \| loan	8
Pre-Modification Unpaid Principal Balance	$ 1
Post-Modification Unpaid Principal Balance	1
Increase (Decrease) in Allowance at Modification	$ 0
Other consumer \| Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Accounts \| loan	6
Pre-Modification Unpaid Principal Balance	$ 0
Post-Modification Unpaid Principal Balance	0
Increase (Decrease) in Allowance at Modification	$ 0

Amount of other addition (reduction) in allowance reserve for credit loss.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Publisher FASB
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