Loans and Leases (Narrative) (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2021 USD ($) contract loan	Mar. 31, 2020 USD ($)	Dec. 31, 2019 loan	Dec. 31, 2020 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 34,344,300,000			$ 33,759,700,000
Other U.S. loans and non-U.S. loans, short duration advances	1,300,000,000			1,100,000,000
Demand deposits	5,600,000			26,400,000
Financing receivable, nonaccrual, interest income	900,000	$ 1,300,000
Financing receivable, nonaccrual troubled debt restructuring	78,800,000			38,900,000
Financing receivable, recorded investment	23,300,000			29,300,000
Financing receivable, troubled debt restructuring, commitment to lend	8,900,000			10,400,000
Foreclosed real estate properties, carrying value	1,500,000			700,000
Loans in process of foreclosure	$ 6,500,000
CARES Act
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, modifications, number of contracts paid off | contract	38
Financing receivable, non-TDR modifications, recorded investment paid off	$ 42,900,000
Paycheck Protection Program
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans approved for forgiveness | loan	219
Loans approved and fully forgiven	$ 34,200,000
Loan processing fee	$ 2,600,000
Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, troubled debt restructuring, subsequent default, number of contracts | loan	1		0
Impaired financing receivable, recorded investment	$ 5,500,000
Impaired financing receivable, unpaid principal balance	5,500,000
Lease Agreements
Accounts, Notes, Loans and Financing Receivable [Line Items]
Held for sale	0			0
Mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Held for sale	0			0
Personal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 18,496,400,000			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%
Collateral required on Residential real estate loan, upper limit	80.00%
Loans and leases	$ 6,066,900,000			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	$ 285,200,000			$ 304,400,000
Percentage of total equity credit lines	97.00%			97.00%
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 15,847,900,000			$ 15,262,000,000.0
Commercial | Commercial and Institutional
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	10,073,100,000			$ 10,058,300,000
Commercial | Commercial and Institutional | Paycheck Protection Program
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 213,900,000
Number of contracts | loan	1,137,000,000
Financing receivable, average balance per loan	$ 200,000