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, 2017	Dec. 31, 2016
Private Equity
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Roll Forward]
Balance at December 31, 2016	$ 33.5	$ 41.9
Return on plan assets:
Unrealized	(1.8)	0.2
Realized	1.0	1.0
Purchases	1.0	1.7
Sales	(9.6)	(11.3)
Balance at December 31, 2017	24.1	33.5
Hedge Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Roll Forward]
Balance at December 31, 2016	33.7	54.0
Return on plan assets:
Unrealized	1.8	0.5
Realized	0.0	0.0
Purchases	0.0	0.0
Sales	(0.5)	(20.8)
Balance at December 31, 2017	35.0	33.7
Real Assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Roll Forward]
Balance at December 31, 2016	19.3	17.4
Return on plan assets:
Unrealized	0.1	0.7
Realized	(0.1)	0.1
Purchases	0.5	2.0
Sales	(1.1)	(0.9)
Balance at December 31, 2017	$ 18.7	$ 19.3