PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS, Additional Disclosures (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Components of net periodic pension cost and weighted-average assumptions used to determine net cost [Abstract]
Service cost (1)	$ 6.2	$ 12.4
Interest cost (2)	$ 28.4	26.4
Settlement loss recognized (2)		5.8
Target rate of return of pension plan investments above inflation rate (in hundredths)	3.00%
Pension benefits [Member]
Components of net periodic pension cost and weighted-average assumptions used to determine net cost [Abstract]
Service cost (1)	$ 6.1	12.3	$ 16.3
Interest cost (2)	27.9	25.5	26.3
Expected return on plan assets (2)	(36.5)	(37.7)	(39.6)
Amortization of net (gain) loss (2)	18.5	23.3	21.0
Prior service amortization	(1.7)	(5.1)	(5.0)
Curtailment gain recognized (2)	(11.4)	0.0	(0.4)
Settlement loss recognized (2)	0.0	0.0	0.5
Net periodic pension cost	$ 2.9	$ 18.3	$ 19.1
Discount rate	3.69%	4.29%	4.53%
Expected return on plan assets	6.68%	7.13%	7.28%
Rate of compensation increase	4.28%	4.14%	4.14%
Other benefits [Member]
Components of net periodic pension cost and weighted-average assumptions used to determine net cost [Abstract]
Service cost (1)	$ 0.1	$ 0.1	$ 0.3
Interest cost (2)	0.5	0.9	1.6
Amortization of net (gain) loss (2)	0.8	0.7	0.3
Prior service amortization	(13.3)	(13.3)	(6.4)
Settlement loss recognized (2)	0.0	5.8	0.1
Net periodic pension cost	$ (11.9)	$ (5.8)	$ (4.1)
Discount rate	3.50%	3.91%	4.18%