Annual report pursuant to Section 13 and 15(d)

BENEFIT PLANS - Fair Value of Pension Assets (Details)

v3.10.0.1
BENEFIT PLANS - Fair Value of Pension Assets (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
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    
Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets $ 533.8 $ 561.1 $ 515.3
Large-Cap Equity | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 64.6 125.5  
Small- and Mid-Cap Equity | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 18.3 39.0  
International Equity | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 90.4 105.1  
Fixed Income | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 281.7 204.0  
Private Equity      
Defined Benefit Plan Disclosure [Line Items]      
Commitments related to investments 9.9 10.7  
Private Equity | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 18.6 24.1  
Hedge Funds | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 34.3 35.0  
Real Assets      
Defined Benefit Plan Disclosure [Line Items]      
Commitments related to investments 0.1 0.5  
Real Assets | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 19.9 18.7  
Cash | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 6.0 9.7  
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 98.9 187.4  
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 64.6 125.5  
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 18.3 39.0  
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 10.0 13.2  
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 6.0 9.7  
Significant Other Observable Inputs (Level 2) | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 362.1 295.9  
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 80.4 91.9  
Significant Other Observable Inputs (Level 2) | Fixed Income | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 281.7 204.0  
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 72.8 77.8  
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 18.6 24.1  
Significant Unobservable Inputs (Level 3) | Hedge Funds | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 34.3 35.0  
Significant Unobservable Inputs (Level 3) | Real Assets | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 19.9 18.7  
Significant Unobservable Inputs (Level 3) | Cash | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets $ 0.0 $ 0.0