Annual report pursuant to Section 13 and 15(d)

BENEFIT PLANS (Reconciliation of Beginning and Ending Balances for Plan Assets Valued using Significant Unobservable Inputs) (Details)

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BENEFIT PLANS (Reconciliation of Beginning and Ending Balances for Plan Assets Valued using Significant Unobservable Inputs) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Private Equity    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Roll Forward]    
Balance at December 31, 2016 $ 33.5 $ 41.9
Return on plan assets:    
Unrealized (1.8) 0.2
Realized 1.0 1.0
Purchases 1.0 1.7
Sales (9.6) (11.3)
Balance at December 31, 2017 24.1 33.5
Hedge Funds    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Roll Forward]    
Balance at December 31, 2016 33.7 54.0
Return on plan assets:    
Unrealized 1.8 0.5
Realized 0.0 0.0
Purchases 0.0 0.0
Sales (0.5) (20.8)
Balance at December 31, 2017 35.0 33.7
Real Assets    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Roll Forward]    
Balance at December 31, 2016 19.3 17.4
Return on plan assets:    
Unrealized 0.1 0.7
Realized (0.1) 0.1
Purchases 0.5 2.0
Sales (1.1) (0.9)
Balance at December 31, 2017 $ 18.7 $ 19.3