Annual report pursuant to Section 13 and 15(d)

BENEFIT PLANS (Benefit Costs Included in Accumulated Other Comprehensive Loss that have not yet Recognized in Net Periodic Pension Cost) (Details)

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BENEFIT PLANS (Benefit Costs Included in Accumulated Other Comprehensive Loss that have not yet Recognized in Net Periodic Pension Cost) (Details) - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]      
Accumulated other comprehensive loss $ 257.5 $ 265.9 $ 245.8
Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Prior service cost, net of accumulated taxes of $2.0 and $3.4 in 2017 and 2016, respectively, for pension benefits and $(0.5) and $(1.2) in 2017 and 2016, respectively, for other benefits 6.3 5.6  
Net actuarial loss, net of accumulated taxes of $91.0 and $143.5 in 2017 and 2016, respectively, for pension benefits and $3.1 and $5.0 in 2017 and 2016, respectively, for other benefits 243.2 254.1  
Impact of Tax Cuts and Jobs Act of 2017 48.7 0.0  
Accumulated other comprehensive loss 298.2 259.7  
Prior service cost, accumulated taxes 2.0 3.4  
Net actuarial loss, accumulated taxes 91.0 143.5  
Other Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Prior service cost, net of accumulated taxes of $2.0 and $3.4 in 2017 and 2016, respectively, for pension benefits and $(0.5) and $(1.2) in 2017 and 2016, respectively, for other benefits (1.8) (2.1)  
Net actuarial loss, net of accumulated taxes of $91.0 and $143.5 in 2017 and 2016, respectively, for pension benefits and $3.1 and $5.0 in 2017 and 2016, respectively, for other benefits 9.8 8.3  
Impact of Tax Cuts and Jobs Act of 2017 1.3 0.0  
Accumulated other comprehensive loss 9.3 6.2  
Prior service cost, accumulated taxes (0.5) (1.2)  
Net actuarial loss, accumulated taxes $ 3.1 $ 5.0