Loans and Leases (Narrative) (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2021 USD ($) loan contract	Jun. 30, 2020 USD ($) loan	Jun. 30, 2021 USD ($) loan	Jun. 30, 2020 USD ($) loan	Dec. 31, 2020 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 37,406,600,000		$ 37,406,600,000		$ 33,759,700,000
Other U.S. loans and non-U.S. loans, short duration advances	1,700,000,000		1,700,000,000		1,100,000,000
Demand deposits	13,300,000		13,300,000		26,400,000
Financing receivable, nonaccrual, interest income	800,000	$ 1,100,000
Interest income that would have been recorded for nonperforming loans			1,700,000
Interest income that would have been recorded for nonperforming loans				$ 2,400,000
Financing receivable, nonaccrual troubled debt restructuring	77,500,000		77,500,000		38,900,000
Financing receivable, recorded investment	27,300,000		27,300,000		29,300,000
Financing receivable, troubled debt restructuring, commitment to lend	9,900,000		9,900,000		10,400,000
Foreclosed real estate properties, carrying value	200,000		200,000		700,000
Loans in process of foreclosure	$ 5,600,000		$ 5,600,000
CARES Act
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, modifications, number of contracts paid off | contract	41
Financing receivable, non-TDR modifications, recorded investment paid off	$ 57,800,000
Paycheck Protection Program
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans approved for forgiveness | loan	889		889
Loans approved and fully forgiven	$ 153,100,000		$ 153,100,000
Loan processing fee			$ 2,700,000
Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, troubled debt restructuring, subsequent default, number of contracts | loan	0	0	0	0
Lease Agreements
Accounts, Notes, Loans and Financing Receivable [Line Items]
Held for sale	$ 0		$ 0		0
Mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Held for sale	131,200,000		131,200,000		0
Personal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 21,198,900,000		$ 21,198,900,000		18,497,700,000
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	$ 6,100,600,000		$ 6,100,600,000		6,035,700,000
Personal | Home Equity Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Draw period for credit line products			10 years
Loans and leases	$ 281,500,000		$ 281,500,000		$ 304,400,000
Percentage of total equity credit lines	97.00%		97.00%		97.00%
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 16,207,700,000		$ 16,207,700,000		$ 15,262,000,000.0
Commercial | Commercial and Institutional
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	9,833,800,000		9,833,800,000		$ 10,058,300,000
Commercial | Commercial and Institutional | Paycheck Protection Program
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 145,400,000		$ 145,400,000
Number of contracts | loan	666,000,000		666,000,000
Financing receivable, average balance per loan	$ 200,000		$ 200,000