STOCK-BASED COMPENSATION PLANS - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Options
Outstanding, beginning of period (in shares)	466,677	983,512	1,098,823
Granted (in shares)	134,450	82,580	65,522
Exercised (in shares)	(4,868)	(582,303)	(166,838)
Canceled (in shares)	(8,235)	(17,112)	(13,995)
Outstanding, end of period (in shares)	588,024	466,677	983,512	1,098,823
Exercisable, end of period (in shares)	383,150
Weighted Average Exercise Price
Outstanding, beginning of period (in dollars per share)	$ 61.04	$ 32.52	$ 35.39
Granted (in dollars per share)	70.44	77.54	86.91
Exercised (in dollars per share)	22.45	28.29	21.37
Canceled (in dollars per share)	73.00	69.76	76.89
Outstanding, end of period (in dollars per share)	63.36	$ 61.04	$ 32.52	$ 35.39
Exercisable, end of period (in dollars per share)	$ 55.25
Weighted Average Remaining Contractual Life
Outstanding (in years)	5 years 8 months 12 days	5 years 8 months 12 days	4 years	4 years 3 months 18 days
Exercisable, end of period (in years)	4 years 8 months 12 days
Aggregate Intrinsic Value
Outstanding, beginning of period	$ 4.3	$ 40.1	$ 52.3
Granted	1.0	0.0	0.0
Exercised	(0.3)	(24.4)	(10.0)
Canceled	0.0	0.0	(0.1)
Outstanding, end of period	8.5	$ 4.3	$ 40.1	$ 52.3
Exercisable, end of period	$ 8.6