EMPLOYEE BENEFITS - Summary of Changes in Plan Assets and Benefit Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Pension and SERP
Net Regulatory Assets [Abstract]
Actuarial (Gain)/Loss Arising During the Year	$ 251.1	$ (431.6)
Actuarial Loss Reclassified as Net Periodic Benefit Expense	(38.8)	(107.0)
Settlement Loss	0.0	0.0
Prior Service Credit Arising During the Year	0.0	0.0
Prior Service (Cost)/Credit Reclassified as Net Periodic Benefit (Expense)/Income	(1.2)	(1.2)
Actuarial Loss	1,101.0	888.7
Prior Service (Credit)/Cost	2.9	4.1
OCI
Actuarial (Gain)/Loss Arising During the Year	14.0	4.6
Actuarial Loss Reclassified as Net Periodic Benefit Expense	(7.0)	(9.0)
Settlement Loss	(12.4)	0.0
Prior Service Credit Arising During the Year	0.0	0.0
Prior Service (Cost)/Credit Reclassified as Net Periodic Benefit (Expense)/Income	(0.1)	(0.2)
Actuarial Loss	56.5	61.9
Prior Service Cost	0.3	0.4
PBOP
Net Regulatory Assets [Abstract]
Actuarial (Gain)/Loss Arising During the Year	(32.0)	36.8
Actuarial Loss Reclassified as Net Periodic Benefit Expense	0.0	0.0
Settlement Loss	0.0	0.0
Prior Service Credit Arising During the Year	(0.9)	0.0
Prior Service (Cost)/Credit Reclassified as Net Periodic Benefit (Expense)/Income	21.8	21.8
Actuarial Loss	49.8	81.8
Prior Service (Credit)/Cost	(87.4)	(108.3)
OCI
Actuarial (Gain)/Loss Arising During the Year	(0.3)	(0.8)
Actuarial Loss Reclassified as Net Periodic Benefit Expense	0.0	0.0
Settlement Loss	0.0	0.0
Prior Service Credit Arising During the Year	0.0	0.0
Prior Service (Cost)/Credit Reclassified as Net Periodic Benefit (Expense)/Income	(0.2)	(0.1)
Actuarial Loss	2.4	2.7
Prior Service Cost	$ 0.7	$ 0.9