ALLOWANCE FOR CREDIT LOSSES ON LOANS AND LEASES - Schedule of Changes in Allowance for Credit Losses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Year	$ 406.0
Charge- Offs	(81.8)	$ (81.1)
Provision for Credit Losses	79.8	71.8	$ 64.0
Balance at End of Year	423.0	406.0
Commercial and industrial
Allowance for Loan and Lease Losses [Roll Forward]
Charge- Offs	(31.9)
Unfunded loan commitment
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Year	21.5	21.4	19.1
Charge- Offs	0.0	0.0	0.0
Recoveries	0.0	0.0	0.0
Net Charge- Offs	0.0	0.0	0.0
Provision for Credit Losses	(0.1)	0.1	2.3
Allowance for PCD Loans and Leases at Acquisition			0.0
Balance at End of Year	21.4	21.5	21.4
Total commercial loans and leases
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Year	279.3	281.7	261.2
Charge- Offs	(64.0)	(68.1)	(23.4)
Recoveries	13.3	9.2	11.0
Net Charge- Offs	(50.7)	(58.9)	(12.4)
Provision for Credit Losses	51.1	56.5	23.4
Allowance for PCD Loans and Leases at Acquisition			9.5
Balance at End of Year	279.7	279.3	281.7
Total commercial loans and leases | Commercial real estate
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Year	166.6	162.1	156.5
Charge- Offs	(38.6)	(12.4)	(12.5)
Recoveries	2.5	4.4	4.1
Net Charge- Offs	(36.1)	(8.0)	(8.4)
Provision for Credit Losses	36.4	12.5	8.0
Allowance for PCD Loans and Leases at Acquisition			6.0
Balance at End of Year	166.9	166.6	162.1
Total commercial loans and leases | Commercial and industrial
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Year	87.8	102.1	87.4
Charge- Offs	(20.9)	(51.2)	(7.4)
Recoveries	9.3	3.8	5.9
Net Charge- Offs	(11.6)	(47.4)	(1.5)
Provision for Credit Losses	9.4	33.1	12.7
Allowance for PCD Loans and Leases at Acquisition			3.5
Balance at End of Year	85.6	87.8	102.1
Total commercial loans and leases | Commercial leases
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Year	21.2	13.5	14.7
Charge- Offs	(0.3)	0.0	(0.1)
Recoveries	0.1	0.0	0.0
Net Charge- Offs	(0.2)	0.0	(0.1)
Provision for Credit Losses	1.9	7.7	(1.1)
Allowance for PCD Loans and Leases at Acquisition			0.0
Balance at End of Year	22.9	21.2	13.5
Total commercial loans and leases | Other
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Year	3.7	4.0	2.6
Charge- Offs	(4.2)	(4.5)	(3.4)
Recoveries	1.4	1.0	1.0
Net Charge- Offs	(2.8)	(3.5)	(2.4)
Provision for Credit Losses	3.4	3.2	3.8
Allowance for PCD Loans and Leases at Acquisition			0.0
Balance at End of Year	4.3	3.7	4.0
Total commercial loans and leases | Unfunded loan commitment
Allowance for Loan and Lease Losses [Roll Forward]
Provision for Credit Losses	0.1	0.3	2.3
Total consumer loans
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Year	126.3	120.0	83.1
Charge- Offs	(17.8)	(13.0)	(8.3)
Recoveries	5.8	4.2	4.5
Net Charge- Offs	(12.0)	(8.8)	(3.8)
Provision for Credit Losses	28.8	15.1	38.4
Allowance for PCD Loans and Leases at Acquisition			2.3
Balance at End of Year	143.1	126.3	120.0
Total consumer loans | Direct installment
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Year	33.8	35.9	26.4
Charge- Offs	(1.8)	(0.6)	(0.6)
Recoveries	1.1	0.6	0.7
Net Charge- Offs	(0.7)	0.0	0.1
Provision for Credit Losses	(4.0)	(2.1)	8.9
Allowance for PCD Loans and Leases at Acquisition			0.5
Balance at End of Year	29.1	33.8	35.9
Total consumer loans | Residential mortgages
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Year	70.5	55.5	33.1
Charge- Offs	(2.6)	(0.7)	(0.6)
Recoveries	1.2	0.5	0.5
Net Charge- Offs	(1.4)	(0.2)	(0.1)
Provision for Credit Losses	26.8	15.2	21.2
Allowance for PCD Loans and Leases at Acquisition			1.3
Balance at End of Year	95.9	70.5	55.5
Total consumer loans | Indirect installment
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Year	12.8	17.3	13.5
Charge- Offs	(11.8)	(10.7)	(6.1)
Recoveries	2.6	2.3	2.2
Net Charge- Offs	(9.2)	(8.4)	(3.9)
Provision for Credit Losses	5.9	3.9	7.7
Allowance for PCD Loans and Leases at Acquisition			0.0
Balance at End of Year	9.5	12.8	17.3
Total consumer loans | Consumer lines of credit
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Year	9.2	11.3	10.1
Charge- Offs	(1.6)	(1.0)	(1.0)
Recoveries	0.9	0.8	1.1
Net Charge- Offs	(0.7)	(0.2)	0.1
Provision for Credit Losses	0.1	(1.9)	0.6
Allowance for PCD Loans and Leases at Acquisition			0.5
Balance at End of Year	8.6	9.2	11.3
Total consumer loans | Unfunded loan commitment
Allowance for Loan and Lease Losses [Roll Forward]
Provision for Credit Losses	(0.2)	(0.2)	0.0
Allowance for credit losses on loans and leases
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Year	405.6	401.7	344.3
Charge- Offs	(81.8)	(81.1)	(31.7)
Recoveries	19.1	13.4	15.5
Net Charge- Offs	(62.7)	(67.7)	(16.2)
Provision for Credit Losses	79.9	71.6	61.8
Allowance for PCD Loans and Leases at Acquisition			11.8
Balance at End of Year	422.8	405.6	401.7
Allowance for credit losses on loans and leases and allowance for unfunded loan commitments
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Year	427.1	423.1	363.4
Charge- Offs	(81.8)	(81.1)	(31.7)
Recoveries	19.1	13.4	15.5
Net Charge- Offs	(62.7)	(67.7)	(16.2)
Provision for Credit Losses	79.8	71.7	64.1
Allowance for PCD Loans and Leases at Acquisition			11.8
Balance at End of Year	$ 444.2	$ 427.1	$ 423.1