Loans Held-for-Investment - Summary of Loans Held-for-Investment (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held-for-investment	$ 13,795	$ 12,129
Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held-for-investment	4,850	4,907
Consumer loans | Residential first mortgage loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held-for-investment	2,964	3,154
Consumer loans | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held-for-investment	1,028	1,024
Consumer loans | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held-for-investment	858	729
Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held-for-investment	8,945	7,222
Commercial loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held-for-investment	3,092	2,828
Commercial loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held-for-investment	1,880	1,634
Commercial loans | Warehouse lending
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held-for-investment	$ 3,973	$ 2,760