Loans (Narrative) (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 42,505,500,000		$ 41,948,300,000
Other U.S. loans and non-U.S. loans, short duration advances	4,400,000,000		4,500,000,000
Demand deposits	5,800,000		12,000,000.0
Loans held for sale	10,000,000.0		6,800,000
Proceeds from sale of loans held-for-sale	22,900,000	$ 0
Interest income, nonaccrual loans	900,000	600,000
Loans in process of foreclosure	6,000,000.0		7,900,000
Loan modifications during period	7,700,000	$ 13,800,000
Modified loans, charged off	0		0
30-89 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified previous 12 months	0		0
90 days or greater past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified previous 12 months	19,000,000.0
Personal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 21,826,700,000		21,517,300,000
Personal | Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collateral required on Residential real estate loan, lower limit	65.00%
Collateral required on Residential real estate loan, upper limit	80.00%
Loans and leases	$ 6,004,500,000		6,121,000,000
Personal | Home Equity Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Draw period for credit line products	10 years
Loans and leases	$ 273,400,000		$ 294,000,000.0
Percentage of total equity credit lines	98.00%		96.00%