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COMMON EQUITY - PERFORMANCE UNITS (Details) - Performance units - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance units granted		8,178	8,500	10,025
Intrinsic value of settled performance units		$ 0.8
Tax benefit from distribution of performance units		$ 0.2
Performance units outstanding		27,692
Liability recorded on balance sheet		$ 2.9
Compensation cost not yet recognized		$ 3.9
Weighted-average period over which unrecognized compensation cost is expected to be recognized		1 year 7 months 6 days
Subsequent event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance units granted	7,017
Intrinsic value of settled performance units	$ 1.8
Tax benefit from distribution of performance units	$ 0.4