Allowance for Credit Losses (Recorded Investments in Loans and Leases) (Details) - USD ($) $ in Millions	Sep. 30, 2022	Jun. 30, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020
Loans and Leases
Evaluated on an Individual Basis	$ 107.9		$ 166.6
Evaluated on a Collective Basis	43,884.0		40,314.0
TOTAL LOANS AND LEASES	43,991.9		40,480.6
Allowance for Credit Losses on Loans and Leases
Evaluated on an Individual Basis	10.9		10.1
Evaluated on a Collective Basis	127.8		128.3
Allowance Assigned to Loans and Leases	138.7	$ 138.2	138.4	$ 143.9	$ 148.8	$ 190.7
Allowance for Undrawn Loan Commitments and Standby Letters of Credit
Evaluated on an Individual Basis	0.0		0.0
Evaluated on a Collective Basis	40.7		34.1
Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit	40.7	43.5	34.1	39.8	46.5	61.1
Total Allowance Assigned to Loans and Leases and Undrawn Loan Commitments and Standby Letters of Credit	179.4		172.5
COMMERCIAL
Loans and Leases
Evaluated on an Individual Basis	64.6		92.1
Evaluated on a Collective Basis	22,724.7		18,395.3
TOTAL LOANS AND LEASES	22,789.3		18,487.4
Allowance for Credit Losses on Loans and Leases
Evaluated on an Individual Basis	10.9		10.1
Evaluated on a Collective Basis	89.7		95.5
Allowance Assigned to Loans and Leases	100.6	102.5	105.6	115.7	118.0	142.2
Allowance for Undrawn Loan Commitments and Standby Letters of Credit
Evaluated on an Individual Basis	0.0		0.0
Evaluated on a Collective Basis	37.5		31.4
Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit	37.5	40.3	31.4	37.2	43.6	57.6
Total Allowance Assigned to Loans and Leases and Undrawn Loan Commitments and Standby Letters of Credit	138.1		137.0
PERSONAL
Loans and Leases
Evaluated on an Individual Basis	43.3		74.5
Evaluated on a Collective Basis	21,159.3		21,918.7
TOTAL LOANS AND LEASES	21,202.6		21,993.2
Allowance for Credit Losses on Loans and Leases
Evaluated on an Individual Basis	0.0		0.0
Evaluated on a Collective Basis	38.1		32.8
Allowance Assigned to Loans and Leases	38.1	35.7	32.8	28.2	30.8	48.5
Allowance for Undrawn Loan Commitments and Standby Letters of Credit
Evaluated on an Individual Basis	0.0		0.0
Evaluated on a Collective Basis	3.2		2.7
Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit	3.2	$ 3.2	2.7	$ 2.6	$ 2.9	$ 3.5
Total Allowance Assigned to Loans and Leases and Undrawn Loan Commitments and Standby Letters of Credit	$ 41.3		$ 35.5