EARNINGS PER-SHARE (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net Income
Net Income, Basic									$ 109.0	$ 231.0	$ 81.4
Net Income, Diluted									$ 109.0	$ 231.0	$ 81.4
Weighted Average Common Shares
Basic (in shares)									42.7	42.9	43.1
Effect of Dilutive Securities (in shares)									0.3	0.3	0.4
Diluted (in shares)									43.0	43.2	43.5
Per Common Share Amount
Net income, Basic (in dollars per share)	$ 0.48	$ 0.97	$ 0.76	$ 0.33	$ 3.90	$ 0.79	$ 0.56	$ 0.16	$ 2.55	$ 5.38	$ 1.89
Effect of Dilutive Securities (in dollars per shares)									(0.02)	(0.03)	(0.02)
Net income, Diluted (in dollars per share)	$ 0.48	$ 0.97	$ 0.76	$ 0.33	$ 3.88	$ 0.79	$ 0.55	$ 0.16	$ 2.53	$ 5.35	$ 1.87