ALLOWANCE FOR CREDIT LOSSES ON LOANS AND LEASES - Changes in Allowance for Credit Losses (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Year	$ 344.0
Provision for credit losses	64.2	$ 0.6	$ 123.0
Balance at End of Year	402.0	344.0
Unfunded loan commitment
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Year	19.1	13.6	3.0
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	2.3	5.5	1.0
Initial ACL on PCD Loans				$ 0.0
Allowance for PCD Loans and Leases at Acquisition	0.0
Balance at End of Year	21.4	19.1	13.6
Unfunded loan commitment | ASC 326 Adoption Impact
Allowance for Loan and Lease Losses [Roll Forward]
ASC 326 Adoption Impact				10.0
Total commercial loans and leases
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Year	261.2	280.4	133.0
Charge- Offs	(23.4)	(27.0)	(68.0)
Recoveries	11.0	15.1	15.0
Net Charge- Offs	(12.4)	(11.9)	(53.0)
Provision for credit losses	23.4	(7.3)	119.0
Initial ACL on PCD Loans				44.0
Allowance for PCD Loans and Leases at Acquisition	9.5
Balance at End of Year	281.7	261.2	280.4
Total commercial loans and leases | ASC 326 Adoption Impact
Allowance for Loan and Lease Losses [Roll Forward]
ASC 326 Adoption Impact				37.0
Total commercial loans and leases | Commercial real estate
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Year	156.5	180.5	60.0
Charge- Offs	(12.5)	(8.8)	(31.0)
Recoveries	4.1	6.3	7.0
Net Charge- Offs	(8.4)	(2.5)	(24.0)
Provision for credit losses	8.0	(21.5)	67.0
Initial ACL on PCD Loans				40.0
Allowance for PCD Loans and Leases at Acquisition	6.0
Balance at End of Year	162.1	156.5	180.5
Total commercial loans and leases | Commercial real estate | ASC 326 Adoption Impact
Allowance for Loan and Lease Losses [Roll Forward]
ASC 326 Adoption Impact				38.0
Total commercial loans and leases | Commercial and industrial
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Year	87.4	81.2	53.0
Charge- Offs	(7.4)	(15.7)	(32.0)
Recoveries	5.9	6.6	7.0
Net Charge- Offs	(1.5)	(9.1)	(25.0)
Provision for credit losses	12.7	15.3	41.0
Initial ACL on PCD Loans				4.0
Allowance for PCD Loans and Leases at Acquisition	3.5
Balance at End of Year	102.1	87.4	81.2
Total commercial loans and leases | Commercial and industrial | ASC 326 Adoption Impact
Allowance for Loan and Lease Losses [Roll Forward]
ASC 326 Adoption Impact				8.0
Total commercial loans and leases | Commercial leases
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Year	14.7	17.3	11.0
Charge- Offs	(0.1)	(0.2)	(1.0)
Recoveries	0.0	0.9	0.0
Net Charge- Offs	(0.1)	0.7	(1.0)
Provision for credit losses	(1.1)	(3.3)	7.0
Initial ACL on PCD Loans				0.0
Allowance for PCD Loans and Leases at Acquisition	0.0
Balance at End of Year	13.5	14.7	17.3
Total commercial loans and leases | Commercial leases | ASC 326 Adoption Impact
Allowance for Loan and Lease Losses [Roll Forward]
ASC 326 Adoption Impact				0.0
Total commercial loans and leases | Other
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Year	2.6	1.4	9.0
Charge- Offs	(3.4)	(2.3)	(4.0)
Recoveries	1.0	1.3	1.0
Net Charge- Offs	(2.4)	(1.0)	(3.0)
Provision for credit losses	3.8	2.2	4.0
Initial ACL on PCD Loans				0.0
Allowance for PCD Loans and Leases at Acquisition	0.0
Balance at End of Year	4.0	2.6	1.4
Total commercial loans and leases | Other | ASC 326 Adoption Impact
Allowance for Loan and Lease Losses [Roll Forward]
ASC 326 Adoption Impact				(9.0)
Total commercial loans and leases | Unfunded loan commitment
Allowance for Loan and Lease Losses [Roll Forward]
Provision for credit losses	2.0	5.0	1.0
Total commercial loans and leases | Unfunded loan commitment | ASC 326 Adoption Impact
Allowance for Loan and Lease Losses [Roll Forward]
ASC 326 Adoption Impact		0.0	0.0	8.0
Total consumer loans
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Year	83.1	82.7	63.0
Charge- Offs	(8.3)	(7.2)	(13.0)
Recoveries	4.5	5.2	6.0
Net Charge- Offs	(3.8)	(2.0)	(7.0)
Provision for credit losses	38.4	2.4	3.0
Initial ACL on PCD Loans				6.0
Allowance for PCD Loans and Leases at Acquisition	2.3
Balance at End of Year	120.0	83.1	82.7
Total consumer loans | ASC 326 Adoption Impact
Allowance for Loan and Lease Losses [Roll Forward]
ASC 326 Adoption Impact				18.0
Total consumer loans | Direct installment
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Year	26.4	26.0	13.0
Charge- Offs	(0.6)	(1.4)	(1.0)
Recoveries	0.7	1.0	1.0
Net Charge- Offs	0.1	(0.4)	0.0
Provision for credit losses	8.9	0.8	2.0
Initial ACL on PCD Loans				1.0
Allowance for PCD Loans and Leases at Acquisition	0.5
Balance at End of Year	35.9	26.4	26.0
Total consumer loans | Direct installment | ASC 326 Adoption Impact
Allowance for Loan and Lease Losses [Roll Forward]
ASC 326 Adoption Impact				10.0
Total consumer loans | Residential mortgages
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Year	33.1	33.7	22.0
Charge- Offs	(0.6)	(1.0)	(2.0)
Recoveries	0.5	0.6	1.0
Net Charge- Offs	(0.1)	(0.4)	(1.0)
Provision for credit losses	21.2	(0.2)	3.0
Initial ACL on PCD Loans				4.0
Allowance for PCD Loans and Leases at Acquisition	1.3
Balance at End of Year	55.5	33.1	33.7
Total consumer loans | Residential mortgages | ASC 326 Adoption Impact
Allowance for Loan and Lease Losses [Roll Forward]
ASC 326 Adoption Impact				6.0
Total consumer loans | Indirect installment
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Year	13.5	11.2	19.0
Charge- Offs	(6.1)	(3.1)	(8.0)
Recoveries	2.2	2.2	4.0
Net Charge- Offs	(3.9)	(0.9)	(4.0)
Provision for credit losses	7.7	3.2	(6.0)
Initial ACL on PCD Loans				0.0
Allowance for PCD Loans and Leases at Acquisition	0.0
Balance at End of Year	17.3	13.5	11.2
Total consumer loans | Indirect installment | ASC 326 Adoption Impact
Allowance for Loan and Lease Losses [Roll Forward]
ASC 326 Adoption Impact				2.0
Total consumer loans | Consumer lines of credit
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Year	10.1	11.8	9.0
Charge- Offs	(1.0)	(1.7)	(2.0)
Recoveries	1.1	1.4	0.0
Net Charge- Offs	0.1	(0.3)	(2.0)
Provision for credit losses	0.6	(1.4)	4.0
Initial ACL on PCD Loans				1.0
Allowance for PCD Loans and Leases at Acquisition	0.5
Balance at End of Year	11.3	10.1	11.8
Total consumer loans | Consumer lines of credit | ASC 326 Adoption Impact
Allowance for Loan and Lease Losses [Roll Forward]
ASC 326 Adoption Impact				0.0
Total consumer loans | Unfunded loan commitment
Allowance for Loan and Lease Losses [Roll Forward]
Provision for credit losses	0.0	0.0	0.0
Total consumer loans | Unfunded loan commitment | ASC 326 Adoption Impact
Allowance for Loan and Lease Losses [Roll Forward]
ASC 326 Adoption Impact		0.0	0.0	2.0
Allowance for credit losses on loans and leases
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Year	344.3	363.1	196.0
Charge- Offs	(31.7)	(34.2)	(81.0)
Recoveries	15.5	20.3	21.0
Net Charge- Offs	(16.2)	(13.9)	(60.0)
Provision for credit losses	61.8	(4.9)	122.0
Initial ACL on PCD Loans				50.0
Allowance for PCD Loans and Leases at Acquisition	11.8
Balance at End of Year	401.7	344.3	363.1
Allowance for credit losses on loans and leases | ASC 326 Adoption Impact
Allowance for Loan and Lease Losses [Roll Forward]
ASC 326 Adoption Impact				55.0
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	363.4	376.7	199.0
Charge- Offs	(31.7)	(34.2)	(81.0)
Recoveries	15.5	20.3	21.0
Net Charge- Offs	(16.2)	(13.9)	(60.0)
Provision for credit losses	64.1	0.6	123.0
Initial ACL on PCD Loans				50.0
Allowance for PCD Loans and Leases at Acquisition	11.8
Balance at End of Year	$ 423.1	$ 363.4	$ 376.7
Allowance for credit losses on loans and leases and allowance for unfunded loan commitments | ASC 326 Adoption Impact
Allowance for Loan and Lease Losses [Roll Forward]
ASC 326 Adoption Impact				$ 65.0