Loans Held-for-Investment - Summary of Newly Modified TDRs (Details) $ in Millions	12 Months Ended
Dec. 31, 2020 USD ($) loan	Dec. 31, 2019 USD ($) loan	Dec. 31, 2018 USD ($) loan
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Accounts \| loan	14,000,000	14	31
Pre-Modification Unpaid Principal Balance	$ 7	$ 1	$ 4
Post-modification unpaid principal balance	7	1	4
Increase (Decrease) in Allowance at Modification	$ 0	$ 0	$ 0
Residential first mortgage
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Accounts \| loan	9,000,000	8	14
Pre-Modification Unpaid Principal Balance	$ 2	$ 1	$ 3
Post-modification unpaid principal balance	2	1	3
Increase (Decrease) in Allowance at Modification	$ 0	$ 0	$ 0
Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Accounts \| loan	3,000,000	6	17
Pre-Modification Unpaid Principal Balance	$ 0	$ 0	$ 1
Post-modification unpaid principal balance	0	0	1
Increase (Decrease) in Allowance at Modification	$ 0	$ 0	$ 0
Other consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Accounts \| loan	1,000,000
Pre-Modification Unpaid Principal Balance	$ 0
Post-modification unpaid principal balance	0
Increase (Decrease) in Allowance at Modification	$ 0
Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Accounts \| loan	1,000,000
Pre-Modification Unpaid Principal Balance	$ 5
Post-modification unpaid principal balance	5
Increase (Decrease) in Allowance at Modification	$ 0

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

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-SubTopic 10
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-Publisher FASB
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