Annual report pursuant to Section 13 and 15(d)

BENEFIT PLANS (Fair Value of Postretirement Assets) (Details)

v3.8.0.1
BENEFIT PLANS (Fair Value of Postretirement Assets) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
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    
Other Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets $ 17.1 $ 16.6 $ 18.9
Other Benefits | Large-Cap Equity      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 4.2 4.5  
Other Benefits | Small- and Mid-Cap Equity      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 1.3 1.1  
Other Benefits | International Equity      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 2.7 2.0  
Other Benefits | Fixed Income      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 6.0 5.4  
Other Benefits | Private Equity      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.8 1.2  
Other Benefits | Hedge Funds      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 1.2 1.2  
Other Benefits | Real Assets      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.6 0.7  
Other Benefits | Cash      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.3 0.5  
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 6.3 6.6  
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Benefits | Large-Cap Equity      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 4.2 4.5  
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Benefits | Small- and Mid-Cap Equity      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 1.3 1.1  
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Benefits | International Equity      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.5 0.5  
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Benefits | Fixed Income      
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) | Other Benefits | Private Equity      
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) | Other Benefits | Hedge Funds      
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) | Other Benefits | Real Assets      
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) | Other Benefits | Cash      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.3 0.5  
Significant Other Observable Inputs (Level 2) | Other Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 8.2 6.9  
Significant Other Observable Inputs (Level 2) | Other Benefits | Large-Cap Equity      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Significant Other Observable Inputs (Level 2) | Other Benefits | Small- and Mid-Cap Equity      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Significant Other Observable Inputs (Level 2) | Other Benefits | International Equity      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 2.2 1.5  
Significant Other Observable Inputs (Level 2) | Other Benefits | Fixed Income      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 6.0 5.4  
Significant Other Observable Inputs (Level 2) | Other Benefits | Private Equity      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Significant Other Observable Inputs (Level 2) | Other Benefits | Hedge Funds      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Significant Other Observable Inputs (Level 2) | Other Benefits | Real Assets      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Significant Other Observable Inputs (Level 2) | Other Benefits | Cash      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Significant Unobservable Inputs (Level 3) | Other Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 2.6 3.1  
Significant Unobservable Inputs (Level 3) | Other Benefits | Large-Cap Equity      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Significant Unobservable Inputs (Level 3) | Other Benefits | Small- and Mid-Cap Equity      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Significant Unobservable Inputs (Level 3) | Other Benefits | International Equity      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Significant Unobservable Inputs (Level 3) | Other Benefits | Fixed Income      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Significant Unobservable Inputs (Level 3) | Other Benefits | Private Equity      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.8 1.2  
Significant Unobservable Inputs (Level 3) | Other Benefits | Hedge Funds      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 1.2 1.2  
Significant Unobservable Inputs (Level 3) | Other Benefits | Real Assets      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.6 0.7  
Significant Unobservable Inputs (Level 3) | Other Benefits | Cash      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets $ 0.0 $ 0.0