Annual report pursuant to Section 13 and 15(d)

PENSION AND OTHER POSTRETIREMENT BENEFITS (Effect of Fair Value Measurements Using Significant Unobservable Inputs (Level 3) on Changes in Other Benefit Plan Assets) (Details)

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PENSION AND OTHER POSTRETIREMENT BENEFITS (Effect of Fair Value Measurements Using Significant Unobservable Inputs (Level 3) on Changes in Other Benefit Plan Assets) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
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
Acquired through business combinations 57.9 8.0
Sales 65.6 14.6
Fair value of plan assets — end of year 215.6 202.4
Hedge Funds [Member]    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
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)
Acquired through business combinations 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]    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
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)
Acquired through business combinations 4.5 8.0
Sales 5.6 6.0
Fair value of plan assets — end of year 39.8 36.1
Real Estate [Member]    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
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
Acquired through business combinations 14.4 0.0
Sales 14.9 0.6
Fair value of plan assets — end of year 65.5 61.9
Other Benefits [Member]    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Fair value of plan assets — beginning of year 253.0 250.6
Actual return on plan assets:    
Fair value of plan assets — end of year 262.5 253.0
Other Benefits [Member] | Hedge Funds [Member]    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Fair value of plan assets — beginning of year 11.2  
Actual return on plan assets:    
Fair value of plan assets — end of year 11.4 11.2
Other Benefits [Member] | Private Equity Funds [Member]    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Fair value of plan assets — beginning of year 4.3  
Actual return on plan assets:    
Fair value of plan assets — end of year 3.9 4.3
Other Benefits [Member] | Structured Credit [Member]    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Fair value of plan assets — beginning of year 6.9  
Actual return on plan assets:    
Fair value of plan assets — end of year 7.9 6.9
Other Benefits [Member] | Real Estate [Member]    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Fair value of plan assets — beginning of year 11.1  
Actual return on plan assets:    
Fair value of plan assets — end of year 12.0 11.1
Significant Unobservable Inputs (Level 3) [Member] | Other Benefits [Member]    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Fair value of plan assets — beginning of year 33.5 32.5
Actual return on plan assets:    
Relating to assets still held at the reporting date 7.1 1.9
Acquired through business combinations 24.0 0.0
Sales 25.5 1.0
Fair value of plan assets — end of year 35.2 33.5
Significant Unobservable Inputs (Level 3) [Member] | Other Benefits [Member] | Hedge Funds [Member]    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Fair value of plan assets — beginning of year 11.2 11.2
Actual return on plan assets:    
Relating to assets still held at the reporting date 0.8 0.0
Acquired through business combinations 17.1 0.0
Sales 17.7 0.0
Fair value of plan assets — end of year 11.4 11.2
Significant Unobservable Inputs (Level 3) [Member] | Other Benefits [Member] | Private Equity Funds [Member]    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Fair value of plan assets — beginning of year 4.3 5.5
Actual return on plan assets:    
Relating to assets still held at the reporting date 0.9 (0.3)
Acquired through business combinations 1.8 0.0
Sales 2.7 1.0
Fair value of plan assets — end of year 3.9 4.3
Significant Unobservable Inputs (Level 3) [Member] | Other Benefits [Member] | Structured Credit [Member]    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Fair value of plan assets — beginning of year 6.9 5.8
Actual return on plan assets:    
Relating to assets still held at the reporting date 2.0 1.1
Acquired through business combinations 2.1 0.0
Sales 2.1 0.0
Fair value of plan assets — end of year 7.9 6.9
Significant Unobservable Inputs (Level 3) [Member] | Other Benefits [Member] | Real Estate [Member]    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Fair value of plan assets — beginning of year 11.1 10.0
Actual return on plan assets:    
Relating to assets still held at the reporting date 3.4 1.1
Acquired through business combinations 3.0 0.0
Sales 3.0 0.0
Fair value of plan assets — end of year $ 12.0 $ 11.1