REGULATORY ASSETS AND LIABILITIES - REGULATORY LIABILITIES (Details) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021
Regulatory liabilities
Other current liabilities	$ 47.9	$ 14.3
Regulatory liabilities	3,947.0	3,946.0
Total regulatory liabilities	3,994.9	3,960.3
Income tax related items
Regulatory liabilities
Total regulatory liabilities	1,959.0	1,998.5
Removal costs
Regulatory liabilities
Total regulatory liabilities	1,255.5	1,248.0
Pension and OPEB benefits
Regulatory liabilities
Total regulatory liabilities	384.0	397.3
Derivatives
Regulatory liabilities
Total regulatory liabilities	241.3	124.1
Energy costs refundable through rate adjustments
Regulatory liabilities
Total regulatory liabilities	45.3	13.7
Uncollectible expense
Regulatory liabilities
Total regulatory liabilities	30.6	37.1
Electric transmission costs
Regulatory liabilities
Total regulatory liabilities	15.9	84.2
Earnings sharing mechanisms
Regulatory liabilities
Total regulatory liabilities	10.1	28.4
Other, net
Regulatory liabilities
Total regulatory liabilities	$ 53.2	$ 29.0