REGULATORY MATTERS - GAS Rate Proceedings and Deferral of Incremental COVID-19 Costs (Details) $ in Millions						1 Months Ended				12 Months Ended
	Jan. 03, 2023 USD ($) rider	Dec. 20, 2022 USD ($)	Aug. 01, 2022 USD ($)	Jan. 01, 2022 USD ($)	Nov. 01, 2020 USD ($)	Nov. 30, 2021 USD ($)	Sep. 30, 2021 USD ($)	Apr. 30, 2021 USD ($)	Feb. 28, 2021	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2021 USD ($)
Public Utilities, General Disclosures [Line Items]
Net regulatory assets											$ 5,833.0		$ 4,711.0
Nicor Gas
Public Utilities, General Disclosures [Line Items]
Public utilities, approved rate increase (decrease), amount						$ 240.0
Authorized ROE						9.75%					9.75%
Public utilities, approved equity capital structure, percentage						54.50%
Nicor Gas | Subsequent Event
Public Utilities, General Disclosures [Line Items]
Authorized ROE	10.35%
Public utilities, approved equity capital structure, percentage	54.50%
Requested rate increase (decrease), amount	$ 321.0
Requested rate increase (decrease), amount related to recovery of investments	$ 59.0
Requested rate increase, projected test year, term	12 months
Requested rate increase (decrease), additional amount	$ 32.0
Requested rate increase (decrease), proposed riders | rider	3
Nicor Gas | Investing In Illinois
Public Utilities, General Disclosures [Line Items]
Public utilities, approved rate increase amount recovery of investments						$ 94.0
Atlanta Gas Light
Public Utilities, General Disclosures [Line Items]
Public utilities, approved rate increase (decrease), amount				$ (43.0)		$ (5.0)
Authorized ROE											10.25%
Public utilities, maximum base rate percentage											5.00%	5.00%
Requested rate increase (decrease), amount												$ 37.6
Requested rate increase, projected test year, term												12 months
Integrated capacity delivery plan, interstate and intrastate capacity asset requirements, term									10 years
Integrated capacity delivery plan, interstate and intrastate capacity asset requirements, detailed plan term									3 years
Integrated capacity delivery plan, capital budgets and related operations and maintenance spending, term								10 years	10 years
Approved rate decrease, percent						10.00%
Integrated capacity delivery plan, capital forecast plan, years one through three						$ 1,700.0
Atlanta Gas Light | Scenario, Forecast
Public Utilities, General Disclosures [Line Items]
Public utilities, approved rate increase (decrease), amount										$ (7.0)
Atlanta Gas Light | Minimum
Public Utilities, General Disclosures [Line Items]
Authorized ROE											10.05%
Integrated capacity delivery plan, capital forecast plan, years one through ten								$ 500.0
Atlanta Gas Light | Maximum
Public Utilities, General Disclosures [Line Items]
Authorized ROE											10.45%
Integrated capacity delivery plan, capital forecast plan, years one through ten								$ 600.0
Virginia Natural Gas
Public Utilities, General Disclosures [Line Items]
Public utilities, approved rate increase (decrease), amount							$ 43.0
Public utilities, approved rate increase amount recovery of investments							$ 14.0
Authorized ROE			10.35%				9.50%				9.50%
Public utilities, approved equity capital structure, percentage			53.20%				51.90%
Requested rate increase (decrease), amount			$ 69.0		$ 50.0
Requested rate increase (decrease), amount related to recovery of investments			$ 15.0
Southern Company Gas [Member]
Public Utilities, General Disclosures [Line Items]
Requested rate increase (decrease), amount		$ 53.0
Net regulatory assets											$ (1,891.0)		$ (1,471.0)