Allowance for Credit Losses (Recorded Investments in Loans and Leases) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Loans and Leases
Evaluated on an Individual Basis	$ 131.7	$ 92.2
Evaluated on a Collective Basis	33,628.0	31,317.4
Lease Financing, net	33,759.7	31,409.6
Allowance for Credit Losses on Credit Exposures
Evaluated on an Individual Basis	9.1	5.0
Evaluated on a Collective Basis	181.6	99.5
Allowance Assigned to Loans and Leases	190.7	104.5	$ 112.6	$ 131.2
Allowance for Undrawn Loan Commitments and Standby Letters of Credit
Evaluated on an Individual Basis	1.6	1.9
Evaluated on a Collective Basis	59.5	18.0
Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit	61.1	19.9	25.6	22.6
Total Allowance Assigned to Loans and Leases and Undrawn Loan Commitments and Standby Letters of Credit	251.8	124.4
Commercial
Loans and Leases
Evaluated on an Individual Basis	66.6	10.4
Evaluated on a Collective Basis	15,195.4	13,990.9
Lease Financing, net	15,262.0
Allowance for Credit Losses on Credit Exposures
Evaluated on an Individual Basis	8.8	3.4
Evaluated on a Collective Basis	133.4	54.7
Allowance Assigned to Loans and Leases	142.2	58.1
Allowance for Undrawn Loan Commitments and Standby Letters of Credit
Evaluated on an Individual Basis	1.6	1.9
Evaluated on a Collective Basis	56.0	13.9
Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit	57.6	15.8
Total Allowance Assigned to Loans and Leases and Undrawn Loan Commitments and Standby Letters of Credit	199.8	73.9
Personal
Loans and Leases
Evaluated on an Individual Basis	65.1	81.8
Evaluated on a Collective Basis	18,432.6	17,326.5
Lease Financing, net	18,497.7
Allowance for Credit Losses on Credit Exposures
Evaluated on an Individual Basis	0.3	1.6
Evaluated on a Collective Basis	48.2	44.8
Allowance Assigned to Loans and Leases	48.5	46.4
Allowance for Undrawn Loan Commitments and Standby Letters of Credit
Evaluated on an Individual Basis	0.0	0.0
Evaluated on a Collective Basis	3.5	4.1
Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit	3.5	4.1
Total Allowance Assigned to Loans and Leases and Undrawn Loan Commitments and Standby Letters of Credit	52.0	50.5
Commercial
Loans and Leases
Lease Financing, net	15,262.0	14,001.3
Allowance for Credit Losses on Credit Exposures
Allowance Assigned to Loans and Leases	142.2	58.1	57.6	63.5
Allowance for Undrawn Loan Commitments and Standby Letters of Credit
Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit	57.6	15.8	21.1	17.3
Personal
Loans and Leases
Lease Financing, net	18,497.7	17,408.3
Allowance for Credit Losses on Credit Exposures
Allowance Assigned to Loans and Leases	48.5	46.4	55.0	67.7
Allowance for Undrawn Loan Commitments and Standby Letters of Credit
Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit	$ 3.5	$ 4.1	$ 4.5	$ 5.3