Loans Held-for-Investment - Summary of Loans Held-for-Investment and UPB of Loan Sales and Purchases in the Loans Held-for-Investment Portfolio (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held-for-investment	$ 15,793		$ 13,408
Total loans sold	0	$ 92
Performing loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans sold	0	$ 92
Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held-for-investment	5,327		3,385
Consumer loans | Residential first mortgage loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held-for-investment	3,147		1,536
Consumer loans | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held-for-investment	769		613
Consumer loans | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held-for-investment	1,411		1,236
Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held-for-investment	10,466		10,023
Commercial loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held-for-investment	3,721		3,223
Commercial loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held-for-investment	3,188		1,826
Commercial loans | Warehouse lending
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held-for-investment	$ 3,557		$ 4,974