PROPERTY, PLANT, AND EQUIPMENT - Ownership and Investment in Jointly-Owned Facilities (Details) $ in Millions	12 Months Ended
Dec. 31, 2022 USD ($) mi	Sep. 30, 2021
Alabama Power
Other Ownership Interests [Line Items]
Percent Ownership	14.00%
Alabama Power \| Greene County (natural gas) Units 1 and 2
Other Ownership Interests [Line Items]
Percent Ownership	60.00%
Plant in Service	$ 193
Accumulated Depreciation	85
CWIP	$ 0
Alabama Power \| Plant Miller (coal) Units 1 and 2
Other Ownership Interests [Line Items]
Percent Ownership	91.80%
Plant in Service	$ 2,148
Accumulated Depreciation	712
CWIP	$ 13
Georgia Power \| Plant Hatch (nuclear)
Other Ownership Interests [Line Items]
Percent Ownership	50.10%
Plant in Service	$ 1,401
Accumulated Depreciation	671
CWIP	$ 62
Georgia Power \| Plant Vogtle (nuclear) Units 1 and 2
Other Ownership Interests [Line Items]
Percent Ownership	45.70%
Plant in Service	$ 3,628
Accumulated Depreciation	2,298
CWIP	$ 94
Georgia Power \| Plant Scherer (coal) Units 1 and 2
Other Ownership Interests [Line Items]
Percent Ownership	8.40%
Plant in Service	$ 276
Accumulated Depreciation	106
CWIP	$ 1
Georgia Power \| Plant Scherer (coal) Unit 3
Other Ownership Interests [Line Items]
Percent Ownership	75.00%
Plant in Service	$ 1,317
Accumulated Depreciation	567
CWIP	$ 6
Georgia Power \| Rocky Mountain (pumped storage)
Other Ownership Interests [Line Items]
Percent Ownership	25.40%
Plant in Service	$ 184
Accumulated Depreciation	153
CWIP	$ 1
Mississippi Power \| Greene County (natural gas) Units 1 and 2
Other Ownership Interests [Line Items]
Percent Ownership	40.00%
Plant in Service	$ 125
Accumulated Depreciation	70
CWIP	$ 0
Mississippi Power \| Plant Daniel (coal) Units 1 and 2
Other Ownership Interests [Line Items]
Percent Ownership	50.00%
Plant in Service	$ 765
Accumulated Depreciation	257
CWIP	$ 30
Southern Company Gas \| Dalton Pipeline (natural gas pipeline)
Other Ownership Interests [Line Items]
Percent Ownership	50.00%
Plant in Service	$ 271
Accumulated Depreciation	23
CWIP	$ 0
Pipeline infrastructure (miles) \| mi	115
Agreement to lease undivided ownership (percent)	50.00%
Future minimum payments receivable	$ 26
Plant Daniel \| Mississippi Power
Other Ownership Interests [Line Items]
Percent Ownership		50.00%

Jointly Owned Utility Plant, Future Minimum Payments Receivable

No definition available.

Name:	so_JointlyOwnedUtilityPlantFutureMinimumPaymentsReceivable
Namespace Prefix:	so_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Pipeline Infrastructure

+ References

No definition available.

+ Details

Name:	so_PipelineInfrastructure
Namespace Prefix:	so_
Data Type:	dtr-types:lengthItemType
Balance Type:	na
Period Type:	instant

- Definition

Undivided Ownership Interest To Be Leased

+ References

No definition available.

+ Details

Name:	so_UndividedOwnershipInterestToBeLeased
Namespace Prefix:	so_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The period end amount owned by the reporting utility of a jointly owned utility plant in service.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 360
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 10.C)
-URI https://asc.fasb.org/extlink&oid=122136288&loc=d3e659983-123033

+ Details

Name:	us-gaap_JointlyOwnedUtilityPlantGrossOwnershipAmountOfPlantInService
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The period end amount of construction work in progress at a jointly owned electricity generation plant.

+ References

+ Details

Name:	us-gaap_JointlyOwnedUtilityPlantOwnershipAmountOfConstructionWorkInProgress
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The period end amount of accumulated depreciation in a jointly owned electricity generation plant.

+ References

+ Details

Name:	us-gaap_JointlyOwnedUtilityPlantOwnershipAmountOfPlantAccumulatedDepreciation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The proportionate share of interest (percent) in a jointly owned utility plant.

+ References

+ Details

Name:	us-gaap_JointlyOwnedUtilityPlantProportionateOwnershipShare
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- 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_OtherOwnershipInterestsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	dei_LegalEntityAxis=so_AlabamaPowerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_JointlyOwnedUtilityPlantAxis=so_GreeneCountyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_JointlyOwnedUtilityPlantAxis=so_PlantMillerCoalUnitsOneAndTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=so_GeorgiaPowerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_JointlyOwnedUtilityPlantAxis=so_PlantHatchNuclearMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_JointlyOwnedUtilityPlantAxis=so_PlantVogtleNuclearUnitsOneAndTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_JointlyOwnedUtilityPlantAxis=so_PlantSchererCoalUnitsOneAndTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_JointlyOwnedUtilityPlantAxis=so_PlantSchererUnitThreeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_JointlyOwnedUtilityPlantAxis=so_RockyMountainPumpedStorageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=so_MississippiPowerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_JointlyOwnedUtilityPlantAxis=so_PlantDanielUnitsOneAndTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=so_SouthernCompanyGasMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_JointlyOwnedUtilityPlantAxis=so_DaltonPipelineNaturalGasPipelineMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PublicUtilityAxis=so_PlantDanielUnits1And2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: