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REGULATORY MATTERS - GAS Infrastructure Replacement Programs and Capital Projects (Details) $ in Millions		1 Months Ended	12 Months Ended
	Nov. 18, 2021 USD ($)	Jun. 30, 2021 USD ($) mi	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2014
Public Utilities, General Disclosures [Line Items]
Capital expenditures related to qualifying projects			$ 7,240	$ 7,441	$ 7,555
Southern Company Gas
Public Utilities, General Disclosures [Line Items]
Capital expenditures related to qualifying projects			1,421	1,471	1,408
Capital expenditures			461
Southern Company Gas \| Steps to Advance Virginia's Energy (SAVE)
Public Utilities, General Disclosures [Line Items]
Capital expenditures			51	49	45
Nicor Gas
Public Utilities, General Disclosures [Line Items]
Capital expenditures related to qualifying projects				$ 389	$ 396
Nicor Gas \| Regulatory Infrastructure Program
Public Utilities, General Disclosures [Line Items]
Program duration period						9 years
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 \| Steps to Advance Virginia's Energy (SAVE)
Public Utilities, General Disclosures [Line Items]
Program duration period					6 years
Approved infrastructure replacement program, approved investment amount, current fiscal year					$ 365
Infrastructure replacement program, approved investment variance amount					5
Virginia Natural Gas \| Steps to Advance Virginia's Energy (SAVE) \| Year 2018
Public Utilities, General Disclosures [Line Items]
Approved infrastructure replacement program, approved investment amount, current fiscal year					35
Virginia Natural Gas \| Steps to Advance Virginia's Energy (SAVE) \| Year 2019
Public Utilities, General Disclosures [Line Items]
Approved infrastructure replacement program, approved investment amount, current fiscal year					40
Virginia Natural Gas \| Steps to Advance Virginia's Energy (SAVE) \| Year 2020
Public Utilities, General Disclosures [Line Items]
Approved infrastructure replacement program, approved investment amount, current fiscal year					50
Virginia Natural Gas \| Steps to Advance Virginia's Energy (SAVE) \| Year 2021
Public Utilities, General Disclosures [Line Items]
Approved infrastructure replacement program, approved investment amount, current fiscal year					60
Virginia Natural Gas \| Steps to Advance Virginia's Energy (SAVE) \| Year 2022
Public Utilities, General Disclosures [Line Items]
Approved infrastructure replacement program, approved investment amount, current fiscal year					70
Virginia Natural Gas \| Steps to Advance Virginia's Energy (SAVE) \| Year 2023
Public Utilities, General Disclosures [Line Items]
Approved infrastructure replacement program, approved investment amount, current fiscal year					70
Virginia Natural Gas \| Steps to Advance Virginia's Energy (SAVE) \| Year 2024
Public Utilities, General Disclosures [Line Items]
Approved infrastructure replacement program, approved investment amount, current fiscal year					$ 70
Atlanta Gas Light
Public Utilities, General Disclosures [Line Items]
Gain contingency, unrecorded amount			91
Annual proceeds from strategic economic development projects			15
Approved annual recovery of capital investment	$ 286
Atlanta Gas Light \| True-Up Recovery, Unrecognized Equity
Public Utilities, General Disclosures [Line Items]
Gain contingency, unrecorded amount			47
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
Operating Segments \| Gas distribution operations \| Southern Company Gas
Public Utilities, General Disclosures [Line Items]
Gross property additions			$ 1,500