BENEFIT PLANS (Components of Net Periodic Benefit Cost- Other Postretirement Benefits) (Details) - Other Postretirement Benefit Plans, Defined Benefit [Member] - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Components of Net Periodic Benefit Cost
Service cost			$ 2.0	$ 2.3	$ 1.2
Service cost				2.2
Interest cost			2.0	0.9	0.5
Amortization of prior service cost (credit)			1.4	(0.3)	(1.5)
Amortization of actuarial gain			(1.5)	(1.3)	(1.4)
Net periodic benefit cost			3.9	1.5	(1.2)
Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income
Net actuarial loss (gain)			3.6	(2.4)	0.9
Prior service cost			0.0	0.0	14.9
Reclassification of prior service credit			(1.4)	0.3	1.5
Reclassification of actuarial gain			1.5	1.3	1.4
Amount recognized in other comprehensive income			3.7	(0.8)	18.7
Amount recognized in net periodic pension benefit cost and other comprehensive income			$ 7.6	$ 0.7	$ 17.5
Assumed Healthcare Cost Trend Rates at December 31
Rate to which the cost trend rate gradually declines	4.50%		4.50%	4.50%	4.50%
Year that the rate reaches the rate it is assumed to maintain			2031	2030	2028
Weighted-average assumptions used to determine net periodic benefit cost for years ended December 31
Discount rate — PBO			5.09%	2.59%	2.19%
Discount rate — service cost	2.84%	2.45%	5.15%	2.89%
Discount rate — interest cost			5.03%	2.06%	1.60%
Weighted-average assumptions used to determine benefit obligation at December 31
Discount rate	2.59%		4.90%	5.08%	2.59%
Pre-65 [Member]
Assumed Healthcare Cost Trend Rates at December 31
Healthcare cost trend rate assumed for next year	6.60%		10.20%	7.04%	6.60%
Post-65 [Member]
Assumed Healthcare Cost Trend Rates at December 31
Healthcare cost trend rate assumed for next year	6.50%				6.50%