XML 169 R127.htm IDEA: XBRL DOCUMENT
v3.24.0.1

REGULATORY MATTERS - MPC System Restoration Rider and Department of Revenue Audit (Details) - USD ($) | 1 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | ---
Jun. 30, 2023 | Jun. 30, 2022 | Jun. 30, 2021 | May 31, 2021 | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021 | Feb. 01, 2024 | Apr. 04, 2023 | Apr. 03, 2023
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |
Reliability reserve, amount deferred |  |  |  |  | $ 63,000,000 | $ 191,000,000 |  |  |  |
Total deferred charges and other assets |  |  |  |  | 19,069,000,000 | 20,148,000,000 |  |  |  |
Regulatory asset |  |  |  |  | 66,000,000 | 216,000,000 |  |  |  |
Major storms |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |
Storm damage reserves accrual |  |  |  |  |  | 239,000,000 | $ 286,000,000 |  |  |
Mississippi Power |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |
Threshold above which actual damages are charged to the reserve (individually exceed) |  |  |  |  | 50,000 |  |  |  |  |
Public utilities, approved rate increase (decrease), amount | $ (7,000,000) | $ 18,000,000 | $ 16,000,000 | $ 28,000,000 |  |  | 9,000,000 |  |  |
Reliability reserve, amount deferred |  |  |  |  | 11,000,000 | 25,000,000 |  |  | $ 11,700,000 | $ 8,300,000
Reliability reserve |  |  |  |  | 36,000,000 | 25,000,000 |  |  |  |
Total deferred charges and other assets |  |  |  |  | 887,000,000 | 828,000,000 |  |  |  |
Regulatory asset |  |  |  |  | 44,000,000 | 36,000,000 |  |  |  |
Mississippi Power | Subsequent Event |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |
Reliability reserve, amount deferred |  |  |  |  |  |  |  | $ 12,600,000 |  |
Mississippi Power | Retail electric revenues |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |
Property damage reserve |  |  |  |  | 45,000,000 | 37,000,000 |  |  |  |
Mississippi Power | Major storms |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |
Storm damage reserves accrual |  |  |  |  | $ 11,700,000 | $ 6,900,000 | $ (1,800,000) |  |  |

X
- Definition Sum of the carrying amounts as of the balance sheet date of all assets, excluding Property, Plant, and Equipment and Other Property and Investments, that are expected to be realized in cash, sold or consumed after one year or beyond the normal operating cycle, if longer. + References No definition available. + Details
Name: | so_DeferredChargesAndOtherAssets
Namespace Prefix: | so_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Property Damage Reserve + References No definition available. + Details
Name: | so_PropertyDamageReserve
Namespace Prefix: | so_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Public Utilities, Deferred Amount, Reliability Reserve + References No definition available. + Details
Name: | so_PublicUtilitiesDeferredAmountReliabilityReserve
Namespace Prefix: | so_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Public Utilities, Reliability Reserve + References No definition available. + Details
Name: | so_PublicUtilitiesReliabilityReserve
Namespace Prefix: | so_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Threshold Above Which Actual Damages Are Charged to the Reserve + References No definition available. + Details
Name: | so_ThresholdAboveWhichActualDamagesAreChargedToReserve
Namespace Prefix: | so_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount, after effects of reinsurance, of increase (decrease) in the liability for unpaid claims and claims adjustment expense. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480081/944-40-50-3 + Details
Name: | us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpensePeriodIncreaseDecrease
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
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 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 The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 980 -SubTopic 340 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org//1943274/2147481878/980-340-50-1 + Details
Name: | us-gaap_RegulatoryAssets
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_LiabilityForCatastropheClaimsByCatastrophicEventAxis=so_MajorStormMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementOperatingActivitiesSegmentAxis=us-gaap_RetailMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |