Annual report pursuant to Section 13 and 15(d)

PENSIONS AND POSTRETIREMENT BENEFITS (Effect of Fair Value Measurements Using Significant Unobservable Inputs (Level 3) on Changes in Pension Plan Assets) (Details)

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PENSIONS AND POSTRETIREMENT BENEFITS (Effect of Fair Value Measurements Using Significant Unobservable Inputs (Level 3) on Changes in Pension Plan Assets) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Roll Forward]    
Fair value of plan assets — beginning of year $ 202.4 $ 193.4
Actual return on plan assets:    
Relating to assets still held at the reporting date 16.1 12.3
Purchases 57.9 8.0
Sales 65.6 14.6
Fair value of plan assets — end of year 215.6 202.4
Hedge Funds [Member]    
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Roll Forward]    
Fair value of plan assets — beginning of year 40.6 40.7
Actual return on plan assets:    
Relating to assets still held at the reporting date 2.5 (0.1)
Purchases 39.0 0.0
Sales 45.1 0.0
Fair value of plan assets — end of year 37.4 40.6
Private Equity Funds [Member]    
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Roll Forward]    
Fair value of plan assets — beginning of year 36.1 33.1
Actual return on plan assets:    
Relating to assets still held at the reporting date 0.3 (2.7)
Purchases 4.5 8.0
Sales 5.6 6.0
Fair value of plan assets — end of year 39.8 36.1
Structured Finance [Member]    
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Roll Forward]    
Fair value of plan assets — beginning of year 63.8 62.1
Actual return on plan assets:    
Relating to assets still held at the reporting date 9.1 10.0
Purchases 0.0 0.0
Sales 0.0 8.0
Fair value of plan assets — end of year 72.9 63.8
Real Estate [Member]    
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Roll Forward]    
Fair value of plan assets — beginning of year 61.9 57.5
Actual return on plan assets:    
Relating to assets still held at the reporting date 4.2 5.1
Purchases 14.4 0.0
Sales 14.9 0.6
Fair value of plan assets — end of year $ 65.5 $ 61.9