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PENSION PLANS AND RETIREMENT BENEFITS (Tables)
3 Months Ended
Mar. 31, 2021
Retirement Benefits [Abstract]  
Components of Net Periodic Benefit (Income) Cost
Pension BenefitsOther Postretirement Benefits
 Three Months Ended March 31,Three Months Ended March 31,
2021202020212020
Components of Net Periodic Benefit (Income) Cost($ in millions)
Service cost$3.0 $3.0 $0.4 $0.3 
Interest cost12.8 18.7 0.3 0.4 
Expected return on plans’ assets(36.1)(35.6)— — 
Amortization of prior service cost(0.1)— — — 
Recognized actuarial loss13.1 11.2 0.7 0.7 
Net periodic benefit (income) cost$(7.3)$(2.7)$1.4 $1.4