Loans and Leases - Collateral-Dependent Loans (Details) $ in Millions	3 Months Ended
	Dec. 31, 2020 USD ($)
C&I
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, collateral for secured borrowings	$ 167
Financing receivable, allowance for credit loss, writeoff, collateral	36
Collateral dependent loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, allowance for credit loss, writeoff, collateral	26
HELOC
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, collateral for secured borrowings	9
RE installment loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, collateral for secured borrowings	$ 26