STOCK-BASED COMPENSATION PLANS (Summary of stock-based compensation expense, net of amounts capitalized) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Pre-tax stock-based compensation expense	$ 4.6	$ 18.1	$ 9.7
Income tax benefit	0.2	3.7	1.7
Stock Options
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Pre-tax stock-based compensation expense	(1.9)	1.4	2.2
Share based compensation costs capitalized	0.2	0.4	2.4
Restricted Stock
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Pre-tax stock-based compensation expense	6.5	16.7	7.5
Share based compensation costs capitalized	$ 0.9	$ 1.0	$ 1.0