REGULATORY ENVIRONMENT - PGL AND NSG 2023 RATE ORDER (Details) - Illinois Commerce Commission (ICC) - 2023 Rate Order - USD ($) $ in Millions		3 Months Ended
	Nov. 16, 2023	Dec. 31, 2023
Public Utilities, General Disclosures [Line Items]
Impairment of property, plant, and equipment		$ 178.9
PGL
Public Utilities, General Disclosures [Line Items]
Approved rate increase	$ 304.6
Approved rate increase (as a percent)	43.50%
Approved return on equity (as a percent)	9.38%
Approved common equity component average (as a percent)	50.79%
Disallowed capital costs	$ 236.2
Impairment of property, plant, and equipment		177.2
NSG
Public Utilities, General Disclosures [Line Items]
Approved rate increase	$ 11.0
Approved rate increase (as a percent)	11.60%
Approved return on equity (as a percent)	9.38%
Approved common equity component average (as a percent)	52.58%
Disallowed capital costs	$ 1.7
Impairment of property, plant, and equipment		$ 1.7