REGULATORY MATTERS - GAS Rate Proceedings and Deferral of Incremental COVID-19 Costs (Details) - USD ($) $ in Millions								1 Months Ended		12 Months Ended
	Feb. 01, 2024	Jan. 01, 2024	Nov. 16, 2023	Aug. 28, 2023	Jan. 01, 2023	Jan. 01, 2022	Nov. 01, 2020	Nov. 30, 2021	Apr. 30, 2021	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Feb. 09, 2024	Dec. 31, 2019
Public Utilities, General Disclosures [Line Items]
Net regulatory assets											$ 6,523	$ 5,833
Nicor Gas
Public Utilities, General Disclosures [Line Items]
Public utilities, approved rate increase (decrease), amount			$ 223					$ 240
Authorized ROE			9.51%					9.75%			9.51%
Public utilities, approved equity capital structure, percentage			50.00%					54.50%
Nicor Gas | Investing In Illinois Qualifying Infrastructure Plant
Public Utilities, General Disclosures [Line Items]
Public utilities, approved rate increase amount recovery of investments								$ 94
Atlanta Gas Light
Public Utilities, General Disclosures [Line Items]
Public utilities, approved rate increase (decrease), amount						$ (43)					$ (7)	(5)
Authorized ROE											10.25%
Public utilities, maximum base rate percentage											5.00%
Integrated capacity delivery plan, capital budgets and related operations and maintenance spending, term									10 years
Approved rate decrease, percent								10.00%
Integrated capacity delivery plan, capital forecast plan, years one through three								$ 1,700
Approved annual recovery of capital investment													$ 286
Atlanta Gas Light | Scenario, Forecast
Public Utilities, General Disclosures [Line Items]
Public utilities, approved rate increase (decrease), amount										$ (9)
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
Atlanta Gas Light | Minimum | Subsequent Event
Public Utilities, General Disclosures [Line Items]
Approved annual recovery of capital investment	$ 700
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
Atlanta Gas Light | Maximum | Subsequent Event
Public Utilities, General Disclosures [Line Items]
Approved annual recovery of capital investment	$ 1,000
Virginia Natural Gas
Public Utilities, General Disclosures [Line Items]
Public utilities, approved rate increase (decrease), amount				$ 48									43
Public utilities, approved rate increase amount recovery of investments													$ 14
Authorized ROE				9.70%							9.70%		9.50%
Public utilities, approved equity capital structure, percentage				49.06%									51.90%
Requested rate increase (decrease), amount					$ 69		$ 50
Virginia Natural Gas | SAVE
Public Utilities, General Disclosures [Line Items]
Approved infrastructure replacement program, approved investment amount, current fiscal year															$ 365
Southern Company Gas
Public Utilities, General Disclosures [Line Items]
Requested rate increase (decrease), amount					$ 53
Net regulatory assets											$ (2,225)	$ (1,891)
Southern Company Gas | Subsequent Event
Public Utilities, General Disclosures [Line Items]
Requested rate increase (decrease), amount		$ 53
Southern Company Gas | SAVE | Subsequent Event
Public Utilities, General Disclosures [Line Items]
Approved infrastructure replacement program, approved investment amount, current fiscal year														$ 355
Southern Company Gas | SAVE | Subsequent Event | 2025
Public Utilities, General Disclosures [Line Items]
Approved infrastructure replacement program, approved investment amount, current fiscal year														$ 70