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Public Utilities, Infrastructure Replacement Programs And Capital Projects, Expenditures

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REGULATORY MATTERS - GAS Infrastructure Replacement Programs and Capital Projects (Details) $ in Millions				3 Months Ended	12 Months Ended
	Feb. 09, 2024 USD ($)	Feb. 01, 2024 USD ($)	Nov. 16, 2023 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2021 USD ($) mi	Dec. 31, 2019 USD ($)	Dec. 31, 2014	Dec. 31, 2022 USD ($)	Dec. 31, 2020 USD ($)
Southern Company Gas
Public Utilities, General Disclosures [Line Items]
Capital expenditures					$ 553.0
Southern Company Gas \| Natural Gas Cost Under Recovery
Public Utilities, General Disclosures [Line Items]
Over (under) recovered fuel cost				$ (214.0)	(214.0)				$ 108.0
Southern Company Gas \| SAVE
Public Utilities, General Disclosures [Line Items]
Capital expenditures					75.0
Southern Company Gas \| SAVE \| Subsequent Event
Public Utilities, General Disclosures [Line Items]
Approved infrastructure replacement program, approved investment amount, current fiscal year	$ 355.0
Program duration period	5 years
Infrastructure replacement program, approved investment variance amount	$ 5.0
Southern Company Gas \| SAVE \| 2025 \| Subsequent Event
Public Utilities, General Disclosures [Line Items]
Approved infrastructure replacement program, approved investment amount, current fiscal year	70.0
Southern Company Gas \| SAVE \| 2026 \| Subsequent Event
Public Utilities, General Disclosures [Line Items]
Approved infrastructure replacement program, approved investment amount, current fiscal year	70.0
Southern Company Gas \| SAVE \| 2027 \| Subsequent Event
Public Utilities, General Disclosures [Line Items]
Approved infrastructure replacement program, approved investment amount, current fiscal year	70.0
Southern Company Gas \| SAVE \| 2028 \| Subsequent Event
Public Utilities, General Disclosures [Line Items]
Approved infrastructure replacement program, approved investment amount, current fiscal year	70.0
Southern Company Gas \| SAVE \| 2029 \| Subsequent Event
Public Utilities, General Disclosures [Line Items]
Approved infrastructure replacement program, approved investment amount, current fiscal year	$ 70.0
Southern Company Gas \| Investing In Illinois Qualifying Infrastructure Plant
Public Utilities, General Disclosures [Line Items]
Capital expenditures					365.0
Nicor Gas
Public Utilities, General Disclosures [Line Items]
Infrastructure disallowed				69.0
Nicor Gas \| Regulatory Infrastructure Program
Public Utilities, General Disclosures [Line Items]
Program duration period								9 years
Nicor Gas \| Investing In Illinois Qualifying Infrastructure Plant
Public Utilities, General Disclosures [Line Items]
Infrastructure disallowed			$ 126.8		63.0		$ 32.0
Capital expenditures							415.0
Nicor Gas \| Other Transmission and Distribution Capital Investments
Public Utilities, General Disclosures [Line Items]
Infrastructure disallowed			$ 95.9
Nicor Gas \| Maximum
Public Utilities, General Disclosures [Line Items]
Infrastructure investment, annual customer rate increase								4.00%
Infrastructure investment, annual customer rate increase in any given year								5.50%
Virginia Natural Gas \| SAVE
Public Utilities, General Disclosures [Line Items]
Approved infrastructure replacement program, approved investment amount, current fiscal year							$ 365.0
Program duration period							6 years
Infrastructure replacement program, approved investment variance amount										$ 5.0
Virginia Natural Gas \| SAVE \| Year 2021
Public Utilities, General Disclosures [Line Items]
Approved infrastructure replacement program, approved investment amount, current fiscal year										60.0
Virginia Natural Gas \| SAVE \| Year 2022
Public Utilities, General Disclosures [Line Items]
Approved infrastructure replacement program, approved investment amount, current fiscal year										70.0
Virginia Natural Gas \| SAVE \| Year 2023
Public Utilities, General Disclosures [Line Items]
Approved infrastructure replacement program, approved investment amount, current fiscal year										70.0
Virginia Natural Gas \| SAVE \| Year 2024
Public Utilities, General Disclosures [Line Items]
Approved infrastructure replacement program, approved investment amount, current fiscal year										$ 70.0
Atlanta Gas Light
Public Utilities, General Disclosures [Line Items]
Gain contingency, unrecorded amount				44.0	44.0
Annual proceeds from strategic economic development projects					15.0
Approved annual recovery of capital investment						$ 286.0
Atlanta Gas Light \| True-Up Recovery, Unrecognized Equity
Public Utilities, General Disclosures [Line Items]
Gain contingency, unrecorded amount				$ 23.0	23.0
Atlanta Gas Light \| Maximum \| Subsequent Event
Public Utilities, General Disclosures [Line Items]
Approved annual recovery of capital investment		$ 1,000.0
Atlanta Gas Light \| Minimum \| Subsequent Event
Public Utilities, General Disclosures [Line Items]
Approved annual recovery of capital investment		$ 700.0
Chattanooga Gas
Public Utilities, General Disclosures [Line Items]
Program duration period						7 years
Pipeline replacement program, length of distribution main \| mi						73
Preliminary estimated cost to complete						$ 118.0
Operating Segments \| Gas distribution operations \| Southern Company Gas
Public Utilities, General Disclosures [Line Items]
Gross property additions					$ 1,600.0