INCOME TAXES - COMPONENTS OF TAX EXPENSE (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Tax Disclosure [Abstract]
Current tax expense	$ 22.0	$ 0.7	$ 42.6	$ 4.8
Deferred tax expense	23.1	29.1	36.9	40.0
Income tax expense calculated based on estimated annual effective tax rate	45.1	29.8	79.5	44.8
Change in valuation allowance	0.0	(7.0)	0.0	(27.0)
Total income tax expense (benefit)	$ 45.1	$ 22.8	$ 79.5	$ 17.8