COMMON EQUITY - RESTRICTED SHARES (Details) - Restricted stock - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Restricted Stock Activity
Outstanding, shares, beginning of period	3,894	7,425
Granted, shares		1,889
Released, shares		(5,288)
Forfeited, shares		(132)
Outstanding, shares, end of period		3,894	7,425
Restricted Stock Weighted-Average Grant Date Fair Value
Outstanding, weighted-average grant date fair value, beginning of period	$ 65.24	$ 58.45
Granted, weighted-average grant date fair value		68.18
Released, weighted-average grant date fair value		56.99
Forfeited, weighted-average grant date fair value		55.48
Outstanding, weighted-average grant date fair value, end of period		$ 65.24	$ 58.45
Restricted Stock - Additional Disclosures
Intrinsic value of released restricted shares		$ 0.4	$ 0.3	$ 0.3
Tax benefit from released restricted shares		0.1	$ 0.1	$ 0.1
Compensation cost not yet recognized		$ 0.4
Weighted-average period over which unrecognized compensation cost is expected to be recognized		1 year 7 months 6 days
Subsequent event
Restricted Stock Activity
Granted, shares	1,622
Restricted Stock Weighted-Average Grant Date Fair Value
Granted, weighted-average grant date fair value	$ 91.49