EMPLOYEE BENEFITS - Summary of Changes in Plan Assets and Benefit Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Pension and SERP
Net Regulatory Assets [Abstract]
Actuarial Loss/(Gain) Arising During the Year	$ 57.0	$ (49.2)
Actuarial (Loss)/Gain Reclassified as Net Periodic Benefit (Expense)/Income	(38.7)	(79.1)
Actuarial (Loss)/Gain Reclassified as Held for Sale	0.0	(16.6)
Actuarial Loss/(Gain) Reclassified from Held for Sale	16.6	0.0
Settlement Loss	0.0	0.0
Prior Service Cost Arising During the Year	0.1	1.3
Prior Service (Cost)/Credit Reclassified as Net Periodic Benefit (Expense)/Income	(1.3)	(1.2)
Prior Service Cost Reclassified as Held for Sale	0.0	(1.2)
Prior Service Cost Reclassified from Held for Sale	1.2	0.0
Actuarial Loss	991.0	956.1
Prior Service (Credit)/Cost	1.8	1.8
OCI
Actuarial Loss/(Gain) Arising During the Year	0.0	2.3
Actuarial (Loss)/Gain Reclassified as Net Periodic Benefit (Expense)/Income	(4.2)	(6.8)
Actuarial (Loss)/Gain Reclassified as Held for Sale	0.0	0.0
Actuarial Loss/(Gain) Reclassified from Held for Sale	0.0	0.0
Settlement Loss	(3.3)	(4.3)
Prior Service Cost Arising During the Year	0.0	0.0
Prior Service (Cost)/Credit Reclassified as Net Periodic Benefit (Expense)/Income	0.2	(0.1)
Prior Service Cost Reclassified as Held for Sale	0.0	0.0
Prior Service Cost Reclassified from Held for Sale	0.0	0.0
Actuarial Loss	40.2	47.7
Prior Service Cost	0.4	0.2
PBOP
Net Regulatory Assets [Abstract]
Actuarial Loss/(Gain) Arising During the Year	(36.8)	(50.9)
Actuarial (Loss)/Gain Reclassified as Net Periodic Benefit (Expense)/Income	0.9	0.4
Actuarial (Loss)/Gain Reclassified as Held for Sale	0.0	7.1
Actuarial Loss/(Gain) Reclassified from Held for Sale	(7.1)	0.0
Settlement Loss	0.0	0.0
Prior Service Cost Arising During the Year	0.0	0.0
Prior Service (Cost)/Credit Reclassified as Net Periodic Benefit (Expense)/Income	21.8	21.8
Prior Service Cost Reclassified as Held for Sale	0.0	(0.6)
Prior Service Cost Reclassified from Held for Sale	0.6	0.0
Actuarial Loss	(36.6)	6.4
Prior Service (Credit)/Cost	(43.8)	(66.2)
OCI
Actuarial Loss/(Gain) Arising During the Year	0.0	(0.6)
Actuarial (Loss)/Gain Reclassified as Net Periodic Benefit (Expense)/Income	0.0	0.0
Actuarial (Loss)/Gain Reclassified as Held for Sale	0.0	0.0
Actuarial Loss/(Gain) Reclassified from Held for Sale	0.0	0.0
Settlement Loss	0.0	0.0
Prior Service Cost Arising During the Year	0.0	0.0
Prior Service (Cost)/Credit Reclassified as Net Periodic Benefit (Expense)/Income	(0.2)	(0.2)
Prior Service Cost Reclassified as Held for Sale	0.0	0.0
Prior Service Cost Reclassified from Held for Sale	0.0	0.0
Actuarial Loss	1.8	1.8
Prior Service Cost	$ 0.3	$ 0.5