EMPLOYEE BENEFITS - CHANGE IN BENEFIT OBLIGATION AND PLAN ASSETS (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Pension Benefits
Change in benefit obligation
Obligation at January 1	$ 773.1	$ 816.2
Service cost	9.0	10.6	$ 9.9
Interest cost	22.7	21.9	25.2
Plan amendments	0.0	0.0
Net transfer from affiliates	0.0	0.0
Actuarial loss (gain)	(204.9)	(37.1)
Participant contributions	0.0	0.0
Benefit payments	(39.2)	(38.5)
Obligation at December 31	560.7	773.1	816.2
Change in fair value of plan assets
Beginning balance at January 1	859.4	816.3
Actual return on plan assets	(135.7)	80.6
Employer contributions	0.6	1.0
Participant contributions	0.0	0.0
Benefit payments	(39.2)	(38.5)
Net transfer from affiliates	0.0	0.0
Ending balance at December 31	685.1	859.4	816.3
Funded status at December 31	124.4	86.3
OPEB Benefits
Change in benefit obligation
Obligation at January 1	146.9	148.5
Service cost	4.0	4.3	4.4
Interest cost	4.4	4.2	5.1
Plan amendments	0.0	(3.5)
Net transfer from affiliates	0.3	0.0
Actuarial loss (gain)	(36.2)	2.3
Participant contributions	0.6	1.1
Benefit payments	(7.8)	(10.0)
Obligation at December 31	112.2	146.9	148.5
Change in fair value of plan assets
Beginning balance at January 1	303.6	288.3
Actual return on plan assets	(41.7)	23.3
Employer contributions	0.9	0.9
Participant contributions	0.6	1.1
Benefit payments	(7.8)	(10.0)
Net transfer from affiliates	0.0	0.0
Ending balance at December 31	255.6	303.6	$ 288.3
Funded status at December 31	$ 143.4	$ 156.7