REGULATORY MATTERS - GAS Infrastructure Replacement Programs and Capital Projects Schedule of QIP (Details) - Nicor Gas - USD ($) $ in Millions		3 Months Ended	12 Months Ended
	Nov. 16, 2023	Dec. 31, 2023	Dec. 31, 2023	Dec. 31, 2019
Commitments [Line Items]
Disallowed		$ 69.0
Investing In Illinois Qualifying Infrastructure Plant
Commitments [Line Items]
Capital Investments			$ 3,228.0
Disallowed	$ 126.8		63.0	$ 32.0
Investing In Illinois Qualifying Infrastructure Plant | Complete
Commitments [Line Items]
Capital Investments			1,246.0
Disallowed			0.0
Investing In Illinois Qualifying Infrastructure Plant | Complete(a)
Commitments [Line Items]
Capital Investments			415.0
Disallowed			32.0
Investing In Illinois Qualifying Infrastructure Plant | Filed March 2021
Commitments [Line Items]
Capital Investments			402.0
Disallowed
Investing In Illinois Qualifying Infrastructure Plant | Filed March 2022
Commitments [Line Items]
Capital Investments			392.0
Disallowed
Investing In Illinois Qualifying Infrastructure Plant | Filed March 2023
Commitments [Line Items]
Capital Investments			408.0
Disallowed			6.0
Investing In Illinois Qualifying Infrastructure Plant | To be filed by March 20, 2024
Commitments [Line Items]
Capital Investments			365.0
Disallowed			$ 25.0