Annual report pursuant to Section 13 and 15(d)

BENEFIT PLANS - Fair Value of Pension Assets (Details)

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BENEFIT PLANS - Fair Value of Pension Assets (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]      
Hedge funds, minimum number of days notice prior to redemption 30 days    
Hedge funds, maximum number of days notice prior to redemption 90 days    
Private Equity Commitments      
Defined Benefit Plan Disclosure [Line Items]      
Commitments related to investments $ 6.0 $ 9.9  
Real Asset Commitments      
Defined Benefit Plan Disclosure [Line Items]      
Commitments related to investments 0.1 0.1  
Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 603.2 533.8 $ 561.1
Large-Cap Equity | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 41.0 64.6  
Small- and Mid-Cap Equity | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 22.7 18.3  
International Equity | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 94.5 90.4  
Fixed Income | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 367.2 281.7  
Private Equity | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 12.9 18.6  
Hedge Funds | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 36.3 34.3  
Real Assets | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 18.9 19.9  
Cash | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 9.7 6.0  
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 73.4 98.9  
Quoted Prices in Active Markets for Identical Assets (Level 1) | Large-Cap Equity | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 41.0 64.6  
Quoted Prices in Active Markets for Identical Assets (Level 1) | Small- and Mid-Cap Equity | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 22.7 18.3  
Quoted Prices in Active Markets for Identical Assets (Level 1) | International Equity | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 10.0  
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed Income | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Quoted Prices in Active Markets for Identical Assets (Level 1) | Private Equity | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Quoted Prices in Active Markets for Identical Assets (Level 1) | Hedge Funds | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Quoted Prices in Active Markets for Identical Assets (Level 1) | Real Assets | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 9.7 6.0  
Significant Other Observable Inputs (Level 2) | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 461.7 362.1  
Significant Other Observable Inputs (Level 2) | Large-Cap Equity | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Significant Other Observable Inputs (Level 2) | Small- and Mid-Cap Equity | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Significant Other Observable Inputs (Level 2) | International Equity | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 94.5 80.4  
Significant Other Observable Inputs (Level 2) | Fixed Income | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 367.2 281.7  
Significant Other Observable Inputs (Level 2) | Private Equity | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Significant Other Observable Inputs (Level 2) | Hedge Funds | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Significant Other Observable Inputs (Level 2) | Real Assets | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Significant Other Observable Inputs (Level 2) | Cash | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Significant Unobservable Inputs (Level 3) | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 68.1 72.8  
Significant Unobservable Inputs (Level 3) | Large-Cap Equity | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Significant Unobservable Inputs (Level 3) | Small- and Mid-Cap Equity | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Significant Unobservable Inputs (Level 3) | International Equity | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Significant Unobservable Inputs (Level 3) | Fixed Income | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Significant Unobservable Inputs (Level 3) | Private Equity | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 12.9 18.6  
Significant Unobservable Inputs (Level 3) | Hedge Funds | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 36.3 34.3  
Significant Unobservable Inputs (Level 3) | Real Assets | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 18.9 19.9  
Significant Unobservable Inputs (Level 3) | Cash | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets $ 0.0 $ 0.0