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, 2018
Dec. 31, 2017
Private Equity    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Roll Forward]    
Balance at December 31, 2017 $ 24.1 $ 33.5
Return on plan assets:    
Unrealized 1.3 (1.8)
Realized 1.7 1.0
Purchases 1.1 1.0
Sales (9.6) (9.6)
Balance at December 31, 2018 18.6 24.1
Hedge Funds    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Roll Forward]    
Balance at December 31, 2017 35.0 33.7
Return on plan assets:    
Unrealized (0.6) 1.8
Realized 0.0 0.0
Purchases 0.0 0.0
Sales (0.1) (0.5)
Balance at December 31, 2018 34.3 35.0
Real Assets    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Roll Forward]    
Balance at December 31, 2017 18.7 19.3
Return on plan assets:    
Unrealized 1.6 0.1
Realized 0.0 (0.1)
Purchases 0.3 0.5
Sales (0.7) (1.1)
Balance at December 31, 2018 $ 19.9 $ 18.7