COMMON EQUITY - STOCK-BASED COMPENSATION EXPENSE (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award
Stock-based compensation expense	$ 2.5	$ 6.3	$ 9.4
Related tax benefit	0.7	1.7	2.6
Stock options
Share Based Compensation Arrangement By Share Based Payment Award
Stock-based compensation expense	1.1	1.0	0.8
Restricted stock
Share Based Compensation Arrangement By Share Based Payment Award
Stock-based compensation expense	1.0	1.2	1.2
Performance units
Share Based Compensation Arrangement By Share Based Payment Award
Stock-based compensation expense	$ 0.4	$ 4.1	$ 7.4