REGULATORY ENVIRONMENT - PGL AND NSG 2023 RATE ORDER (Details) - Illinois Commerce Commission (ICC) - 2023 Rate Order - USD ($) $ in Millions			3 Months Ended
	May 30, 2024	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	$ 1.6	$ 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
Additional capital spend approved	$ 28.5
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