Loans (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 42,949,400,000		$ 42,949,400,000		$ 43,390,600,000
Other U.S. loans and non-U.S. loans, short duration advances	4,700,000,000		4,700,000,000		3,800,000,000
Demand deposits	7,400,000		7,400,000		47,600,000
Loans held for sale					0
Proceeds from sale of loans held-for-sale	3,100,000	$ 0	3,100,000	$ 0
Interest income, nonaccrual loans	1,200,000	500,000	3,100,000	1,700,000
Loans in process of foreclosure	3,400,000		3,400,000		3,500,000
Loan modifications during period	11,400,000		44,100,000
Modified loans, charged off	2,000,000	0	2,100,000	8,500,000
30-89 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified previous 12 months	18,400,000	0	18,400,000	0
90 days or greater past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified previous 12 months	0	$ 1,000,000	0	$ 1,000,000
Personal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 22,378,300,000		$ 22,378,300,000		23,111,800,000
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	$ 6,045,600,000		$ 6,045,600,000		6,109,900,000
Personal | Home Equity Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Draw period for credit line products			10 years
Loans and leases	$ 266,800,000		$ 266,800,000		$ 250,300,000
Percentage of total equity credit lines			98.00%		97.00%