EMPLOYEE BENEFITS - Summary of Changes in Plan Assets and Benefit Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Pension and SERP
Net Regulatory Assets [Abstract]
Actuarial (Gains)/Losses Arising During the Year	$ (431.6)	$ (961.7)
Actuarial Losses Reclassified as Net Periodic Benefit Expense	(107.0)	(231.2)
Prior Service (Cost)/Credit Reclassified as Net Periodic Benefit (Expense)/Income	(1.2)	(1.3)
Actuarial Loss	888.7	1,427.3
Prior Service (Credit)/Cost	4.1	5.3
OCI
Actuarial (Gains)/Losses Arising During the Year	4.6	(28.4)
Actuarial Losses Reclassified as Net Periodic Benefit Expense	(9.0)	(12.7)
Prior Service (Cost)/Credit Reclassified as Net Periodic Benefit (Expense)/Income	(0.2)	(0.1)
Actuarial Loss	61.9	66.3
Prior Service Cost	0.4	0.6
PBOP
Net Regulatory Assets [Abstract]
Actuarial (Gains)/Losses Arising During the Year	36.8	(181.5)
Actuarial Losses Reclassified as Net Periodic Benefit Expense	0.0	(8.5)
Prior Service (Cost)/Credit Reclassified as Net Periodic Benefit (Expense)/Income	21.8	21.1
Actuarial Loss	81.8	45.0
Prior Service (Credit)/Cost	(108.3)	(130.1)
OCI
Actuarial (Gains)/Losses Arising During the Year	(0.8)	(4.0)
Actuarial Losses Reclassified as Net Periodic Benefit Expense	0.0	(0.4)
Prior Service (Cost)/Credit Reclassified as Net Periodic Benefit (Expense)/Income	(0.1)	0.1
Actuarial Loss	2.7	3.5
Prior Service Cost	$ 0.9	$ 1.0