Loans and Allowance for Loan Losses - Transfers From Loans Held-For-Sale to Loans Held-For-Investment (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized Cost	$ 41
Valuation Allowance Reversed for LHFS	0
Allowance for Loan Losses Established for LHFI	0
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized Cost	36
Valuation Allowance Reversed for LHFS	0
Allowance for Loan Losses Established for LHFI	0
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized Cost	5
Valuation Allowance Reversed for LHFS	0
Allowance for Loan Losses Established for LHFI	$ 0