NET INCOME PER COMMON SHARE (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Basic and Diluted EPS Numerator:
Net income	$ 83.0	$ 68.0	$ 201.1	$ 83.2
Net loss attributable to redeemable noncontrolling interest	0.3	0.3	0.6	0.6
Net income excluding redeemable noncontrolling interest	83.3	68.3	201.7	83.8
Change in redemption value of redeemable noncontrolling interest	(0.3)	(0.3)	(0.6)	(0.6)
Net income allocated to participating securities	(0.6)	(0.7)	(1.4)	(0.8)
Net income allocated to common stockholders	$ 82.4	$ 67.3	$ 199.7	$ 82.4
Basic EPS Denominator:
Weighted average shares outstanding (in shares)	112.0	112.1	112.2	102.1
Basic Net Income Per Common Share (in dollars per share)	$ 0.74	$ 0.60	$ 1.78	$ 0.81
Diluted EPS Denominator:
Weighted average shares outstanding (in shares)	112.0	112.1	112.2	102.1
Dilutive common shares issued under stock program (in shares)	0.3	0.4	0.4	0.2
Total dilutive weighted average shares (in shares)	112.3	112.5	112.6	102.3
Diluted Net Income Per Common Share (in dollars per share)	$ 0.73	$ 0.60	$ 1.77	$ 0.81