Loans (Narrative) (Details) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 43,546,700,000		$ 43,546,700,000		$ 42,893,300,000
Other U.S. loans and non-U.S. loans, short duration advances	3,700,000,000		3,700,000,000		2,900,000,000
Demand deposits	8,600,000		8,600,000		24,400,000
Loan processing fee	0	$ 10,600,000	0	$ 11,200,000
Financing receivable, nonaccrual, interest income	700,000	$ 1,000,000	1,400,000	$ 2,100,000
Loans in process of foreclosure	1,300,000		1,300,000		1,100,000
Modified loans, charged off			700,000
Nonaccrual loans, troubled debt restructurings					35,300,000
Accrual troubled debt restructurings					39,700,000
Troubled debt restructuring, commitment to lend					200,000
Mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, held-for-sale, not part of disposal group, after valuation allowance	0		0		0
Personal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 21,185,500,000		$ 21,185,500,000		21,257,700,000
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	$ 6,357,900,000		$ 6,357,900,000		6,413,500,000
Personal | Home Equity Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Draw period for credit line products			10 years
Loans and leases	228,800,000		$ 228,800,000		$ 248,600,000
Percentage of total equity credit lines			98.00%		98.00%
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 22,361,200,000		$ 22,361,200,000		$ 21,635,600,000