Annual report pursuant to Section 13 and 15(d)

PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Unobservable Inputs, Level 3) (Details)

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PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Unobservable Inputs, Level 3) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets $ 215.6 $ 202.4 $ 193.4
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held 16.1 12.3  
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Sold 4.8 3.3  
Defined Benefit Plan, Plan Assets, Business Combination 57.9 8.0  
Defined Benefit Plan, Plan Assets, Divestiture (65.6) (14.6)  
Other Postretirement Benefit Plan, Defined Benefit [Member]      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets 262.5 253.0 250.6
Private Equity Funds [Member]      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets 39.8 36.1 33.1
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held 0.3 (2.7)  
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Sold 4.5 3.7  
Defined Benefit Plan, Plan Assets, Business Combination 4.5 8.0  
Defined Benefit Plan, Plan Assets, Divestiture (5.6) (6.0)  
Private Equity Funds [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets 3.9 4.3  
Structured Finance [Member]      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets 72.9 63.8 62.1
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held 9.1 10.0  
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Sold 0.0 (0.3)  
Defined Benefit Plan, Plan Assets, Business Combination 0.0 0.0  
Defined Benefit Plan, Plan Assets, Divestiture 0.0 (8.0)  
Real Estate [Member]      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets 65.5 61.9 57.5
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held 4.2 5.1  
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Sold (0.1) (0.1)  
Defined Benefit Plan, Plan Assets, Business Combination 14.4 0.0  
Defined Benefit Plan, Plan Assets, Divestiture (14.9) (0.6)  
Real Estate [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets 12.0 11.1  
Structured Credit [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets 7.9 6.9  
Hedge Funds [Member]      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets 37.4 40.6 40.7
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held 2.5 (0.1)  
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Sold 0.4 0.0  
Defined Benefit Plan, Plan Assets, Business Combination 39.0 0.0  
Defined Benefit Plan, Plan Assets, Divestiture (45.1) 0.0  
Hedge Funds [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets 11.4 11.2  
Fair Value, Inputs, Level 3 [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets 35.2 33.5 32.5
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held 7.1 1.9  
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Sold (3.9) 0.1  
Defined Benefit Plan, Plan Assets, Business Combination 24.0 0.0  
Defined Benefit Plan, Plan Assets, Divestiture (25.5) (1.0)  
Fair Value, Inputs, Level 3 [Member] | Private Equity Funds [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets 3.9 4.3 5.5
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held 0.9 (0.3)  
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Sold (0.4) 0.1  
Defined Benefit Plan, Plan Assets, Business Combination 1.8 0.0  
Defined Benefit Plan, Plan Assets, Divestiture (2.7) (1.0)  
Fair Value, Inputs, Level 3 [Member] | Real Estate [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets 12.0 11.1 10.0
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held 3.4 1.1  
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Sold (2.5) 0.0  
Defined Benefit Plan, Plan Assets, Business Combination 3.0 0.0  
Defined Benefit Plan, Plan Assets, Divestiture (3.0) 0.0  
Fair Value, Inputs, Level 3 [Member] | Structured Credit [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets 7.9 6.9 5.8
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held 2.0 1.1  
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Sold (1.0) 0.0  
Defined Benefit Plan, Plan Assets, Business Combination 2.1 0.0  
Defined Benefit Plan, Plan Assets, Divestiture (2.1) 0.0  
Fair Value, Inputs, Level 3 [Member] | Hedge Funds [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets 11.4 11.2 $ 11.2
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held 0.8 0.0  
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Sold 0.0 0.0  
Defined Benefit Plan, Plan Assets, Business Combination 17.1 0.0  
Defined Benefit Plan, Plan Assets, Divestiture $ (17.7) $ 0.0