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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 |  |  |

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