Loans (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 43,577,000,000		$ 43,577,000,000		$ 42,893,300,000
Other U.S. loans and non-U.S. loans, short duration advances	4,200,000,000		4,200,000,000		2,900,000,000
Demand deposits	4,500,000		4,500,000		24,400,000
Loan processing fee	0	$ 0	0	$ 11,200,000
Financing receivable, nonaccrual, interest income	900,000	$ 1,100,000	2,300,000	$ 3,200,000
Loans in process of foreclosure	1,100,000		1,100,000		1,100,000
Financing receivable, excluding accrued interest, modified, write-off, borrowers with financial difficulty			0
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	$ 21,589,700,000		$ 21,589,700,000		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	$ 6,285,800,000		$ 6,285,800,000		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	228,100,000		$ 228,100,000		$ 248,600,000
Percentage of total equity credit lines			97.00%		98.00%
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 21,987,300,000		$ 21,987,300,000		$ 21,635,600,000