Loans Held-for-Investment - Summary of Loans Held-for-Investment (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held-for-investment	$ 16,227	$ 12,129
Total consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held-for-investment		4,907
Total commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held-for-investment	12,101	7,222
Total consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held-for-investment	4,126	4,907
Total consumer loans | Residential first mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held-for-investment	2,266	3,154
Total consumer loans | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held-for-investment	856	1,024
Total consumer loans | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held-for-investment	1,004	729
Total commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held-for-investment	12,101	7,222
Total commercial loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held-for-investment	3,061	2,828
Total commercial loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held-for-investment	1,382	1,634
Total commercial loans | Warehouse lending
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held-for-investment	$ 7,658	$ 2,760