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, 2018
Dec. 31, 2017
Dec. 31, 2016
Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Service cost $ 3.6 $ 4.0 $ 3.6
Interest cost 26.4 28.5 31.3
Expected return on plan assets (37.5) (37.4) (37.6)
Amortization of prior service cost 0.5 0.6 0.8
Recognized actuarial loss (gain) 19.7 15.5 13.6
Total net periodic benefit cost (income) 12.7 11.2 11.7
Other Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Service cost 0.4 0.4 0.3
Interest cost 0.8 0.9 0.8
Expected return on plan assets (1.1) (1.2) (1.4)
Amortization of prior service cost (1.0) (1.0) (1.1)
Recognized actuarial loss (gain) 1.4 1.3 0.8
Total net periodic benefit cost (income) $ 0.5 $ 0.4 $ (0.6)