PENSION AND POST-RETIREMENT PLANS - AMOUNTS INCLUDED IN FINANCIAL STATEMENTS (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Employee benefit plans
Non-current assets	$ 34.8	$ 18.9
Non-current liabilities	(21.8)	(17.8)
Pension Benefits
Employee benefit plans
Projected benefit obligations	193.1	187.4	$ 249.5
Fair value of plan assets at end of year	227.9	206.3	238.9
Pension Benefits | Qualified Plan
Employee benefit plans
Non-current assets	34.8	18.9
Total	34.8	18.9
Net (loss) gain, net of taxes	(20.3)	(25.8)
Total	(20.3)	(25.8)
Pension Benefits | Nonqualified Plan
Employee benefit plans
Current liabilities	(1.2)	(0.7)
Non-current liabilities	(3.4)	(3.4)
Total	(4.6)	(4.1)
Net (loss) gain, net of taxes	(0.2)	0.1
Total	(0.2)	0.1
Post-retirement benefits
Employee benefit plans
Projected benefit obligations	$ 19.5	15.3	$ 29.3
Amortization period of unrecognized gains and losses	5 years
Post-retirement benefits | Qualified Plan
Employee benefit plans
Current liabilities	$ (1.1)	(0.9)
Non-current liabilities	(18.4)	(14.4)
Total	(19.5)	(15.3)
Net (loss) gain, net of taxes	2.7	7.6
Prior service credit, net of taxes	8.3	11.1
Total	$ 11.0	$ 18.7