Annual report pursuant to Section 13 and 15(d)

BENEFIT PLANS - Components of Net Periodic Benefit Cost (Details)

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BENEFIT PLANS - Components of Net Periodic Benefit Cost (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]      
Recognized actuarial loss (gain) - mark to market $ (0.1) $ (1.4)  
Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Service cost 1.2 1.5 $ 1.4
Interest cost 27.4 20.1 19.0
Expected return on plan assets (22.8) (24.8) (28.7)
Amortization of prior service cost 0.4 (1.7) (1.8)
Recognized actuarial loss (gain) - mark to market 1.9 (2.7) 21.0
Settlements 0.0 (1.0) 0.0
Total net periodic benefit cost (income) 8.1 (8.6) 10.9
Other Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Service cost 0.1 0.2 0.2
Interest cost 0.7 0.5 0.5
Expected return on plan assets (0.6) (0.7) (0.7)
Amortization of prior service cost (0.5) (0.5) (0.1)
Recognized actuarial loss (gain) - mark to market (1.8) 0.5 (0.8)
Settlements 0.0 0.0 0.0
Total net periodic benefit cost (income) $ (2.1) $ 0.0 $ (0.9)