EARNINGS PER-SHARE (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net Income
Net Income, Basic									$ 193.1	$ 82.7	$ 109.0
Net Income, Diluted									$ 193.1	$ 82.7	$ 109.0
Weighted Average Common Shares
Basic									43.1	42.8	42.7
Effect of Dilutive Securities (in shares)									0.4	0.5	0.3
Diluted (in shares)									43.5	43.3	43.0
Per Common Share Amount
Net income, Basic (in dollars per share)	$ 1.99	$ 1.65	$ 0.76	$ 0.09	$ 0.36	$ 0.84	$ 0.43	$ 0.29	$ 4.48	$ 1.93	$ 2.55
Effect of Dilutive Securities (in dollars per shares)									(0.04)	(0.02)	(0.02)
Net income, Diluted (in dollars per share)	$ 1.96	$ 1.63	$ 0.76	$ 0.09	$ 0.36	$ 0.84	$ 0.43	$ 0.29	$ 4.44	$ 1.91	$ 2.53