Loans and Leases (Narrative) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) loan	Mar. 31, 2019 loan	Sep. 30, 2020 USD ($) loan contract	Dec. 31, 2019 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 32,766,300,000		$ 32,766,300,000	$ 31,409,600,000
Other U.S. loans and non-U.S. loans, short duration advances	1,300,000,000		1,300,000,000	1,100,000,000
Demand deposits	11,600,000		11,600,000	90,400,000
Financing receivable, nonaccrual troubled debt restructuring	67,500,000		67,500,000	54,900,000
Financing receivable, recorded investment	33,000,000.0		33,000,000.0	27,700,000	$ 1,700,000	$ 1,600,000
Financing receivable, troubled debt restructuring, commitment to lend	11,000,000.0		11,000,000.0	8,200,000
Foreclosed real estate properties, carrying value	900,000		900,000	3,200,000
Loans in process of foreclosure	11,700,000		$ 11,700,000
CARES Act
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, modifications, number of contracts paid off | contract			31
Financing receivable, non-TDR modifications, recorded investment paid off			$ 34,300,000
Paycheck Protection Program
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 215,300,000		215,300,000
Loan processing fee			$ 2,600,000
Number of loans approved for forgiveness | loan	0		0
Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, troubled debt restructuring, subsequent default, number of contracts | loan	0	3	0
Lease Agreements
Accounts, Notes, Loans and Financing Receivable [Line Items]
Held for sale	$ 18,600,000		$ 18,600,000	53,600,000
Mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Held for sale	0		0	0
Personal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 18,184,600,000		$ 18,184,600,000	17,408,300,000
Personal | Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collateral required on Residential real estate loan, lower limit	65.00%		65.00%
Collateral required on Residential real estate loan, upper limit	80.00%		80.00%
Loans and leases	$ 5,928,300,000		$ 5,928,300,000	6,095,000,000.0
Personal | Home Equity Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Draw period for credit line products			10 years
Loans and leases	$ 351,800,000		$ 351,800,000	$ 448,500,000
Percentage of total equity credit lines	97.00%		97.00%	97.00%
COMMERCIAL
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 14,581,700,000		$ 14,581,700,000	$ 14,001,300,000
COMMERCIAL | Commercial and Institutional
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	9,524,000,000.0		9,524,000,000.0	$ 9,091,100,000
COMMERCIAL | Commercial and Institutional | Paycheck Protection Program
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 215,300,000		$ 215,300,000
Number of contracts | loan	1,127,000,000		1,127,000,000
Financing receivable, average balance per loan	$ 200,000		$ 200,000