CREDIT LOSSES - GROSS RECEIVABLES AND RELATED ALLOWANCES (Details) - USD ($) $ in Millions	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Utility segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable and unbilled revenues	$ 637.2		$ 525.4
Allowance for credit losses	71.3	$ 78.8	59.3	$ 45.7	$ 39.8	$ 38.1
Accounts receivable and unbilled revenues, net	565.9		466.1
Total accounts receivable, net - past due greater than 90 days	$ 39.6		$ 56.3
Past due greater than 90 days - collection risk mitigated by regulatory mechanisms	95.60%		98.20%
Amount of net accounts receivable with regulatory protections	$ 219.9
Percent of net accounts receivable with regulatory protections	38.90%
Other Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable and unbilled revenues	$ 0.0		$ 0.0