PROPERTY, PLANT, AND EQUIPMENT - PLANT TO BE RETIRED (Details) $ in Millions	Mar. 31, 2024 USD ($) MW	Sep. 30, 2023 MW	Jun. 30, 2023 MW
WE | OCPP
Property, plant, and equipment
Net book value of plant to be retired	$ 760.0
WE | West Riverside Energy Center
Property, plant, and equipment
Capacity of generation unit | MW	200	100	100
WPS | Columbia Energy Center
Property, plant, and equipment
Net book value of plant to be retired	$ 255.2