REGULATORY ENVIRONMENT - PGL QIP RIDER (Details) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2025 USD ($) Assurance	Sep. 30, 2024 USD ($)	Jun. 30, 2024 USD ($)	Jun. 30, 2025 USD ($) Assurance	Jun. 30, 2024 USD ($)	Aug. 31, 2024 USD ($)
Public Utilities, General Disclosures [Line Items]
Pre-tax charge to income	$ (262.5)		$ (251.6)	$ (1,048.7)	$ (961.9)
Reduction in revenues	(2,009.5)		(1,772.0)	(5,159.0)	(4,452.2)
Operation and maintenance expense	596.2		533.4	1,204.2	1,064.2
Interest expense	220.8		$ 200.6	443.8	$ 392.6
Illinois Commerce Commission (ICC) | PGL | 2016 Annual QIP Rider Reconciliation
Public Utilities, General Disclosures [Line Items]
Disallowed capital costs						$ 14.8
Pre-tax charge to income		$ 25.3
Reduction in revenues		12.9
Operation and maintenance expense		12.1
Interest expense		$ 0.3
Illinois Commerce Commission (ICC) | PGL | QIP Rider Open Reconciliations 2017-2023
Public Utilities, General Disclosures [Line Items]
Aggregate capital costs during open reconciliation years	$ 2,900.0			$ 2,900.0
Amount of assurance that QIP rider costs will be recoverable | Assurance	0			0