REGULATORY ENVIRONMENT - PGL AND NSG UEA RIDER (Details) - Illinois Commerce Commission (ICC) $ in Millions	1 Months Ended
	May 31, 2023 USD ($)	Jun. 30, 2025 USD ($) Assurance
Uncollectible Expense Adjustment Rider Open Reconciliations 2019-2024
Public Utilities, General Disclosures [Line Items]
Amount of assurance that UEA rider costs will be recoverable | Assurance		0
Minimum annual costs included in UEA rider during open reconciliation years		$ 10.0
Maximum annual costs included in UEA rider during open reconciliation years		$ 40.0
PGL | 2018 Annual Uncollectible Expense Adjustment Rider Reconciliation
Public Utilities, General Disclosures [Line Items]
Refunds required to customers	$ 15.4
Refund period	9 months
NSG | 2018 Annual Uncollectible Expense Adjustment Rider Reconciliation
Public Utilities, General Disclosures [Line Items]
Refunds required to customers	$ 0.7
Refund period	9 months