XML 115 R84.htm IDEA: XBRL DOCUMENT
v3.25.3

Regulatory Matters - Southern Company Gas (Details) - USD ($) $ in Millions | Aug. 12, 2025 | Mar. 26, 2025
--- | --- | ---
Nicor Gas | Investing In Illinois Qualifying Infrastructure Plant |  |
Public Utilities, General Disclosures [Line Items] |  |
Capital expenditures disallowed |  | $ 14
Virginia Natural Gas | SAVE Program |  |
Public Utilities, General Disclosures [Line Items] |  |
Approved rate increase (decrease) | $ 40 |
ROE | 9.85% |
Equity ratio | 49.35% |
Requested rate increase amount | $ 63 |

X
- Definition Public Utilities, Infrastructure Replacement Programs And Capital Projects, Expenditures Disallowed + References No definition available. + Details
Name: | so_PublicUtilitiesInfrastructureReplacementProgramsAndCapitalProjectsExpendituresDisallowed
Namespace Prefix: | so_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Percentage of public utility's approved equity to capital, including debt and equity. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesApprovedEquityCapitalStructurePercentage
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of public utility's approved rate increase (decrease) by regulatory agency. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesApprovedRateIncreaseDecreaseAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Percentage of public utility's approved return on equity. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesApprovedReturnOnEquityPercentage
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesGeneralDisclosuresLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of public utility's requested rate increase (decrease) with regulatory agency. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesRequestedRateIncreaseDecreaseAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | dei_LegalEntityAxis=so_NicorGasMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | so_ProgramAxis=so_InvestingInIllinoisQualifyingInfrastructurePlantMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=so_VirginiaNaturalGasMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | so_ProgramAxis=so_SAVEProgramMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |