Proceeds From Asset Acquisition, Transaction Cost Reimbursement

No definition available.

Name:	so_ProceedsFromAssetAcquisitionTransactionCostReimbursement
Namespace Prefix:	so_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Public Utilities, Approved Additional Generating Capacity

+ References

No definition available.

+ Details

Name:	so_PublicUtilitiesApprovedAdditionalGeneratingCapacity
Namespace Prefix:	so_
Data Type:	dtr-types:powerItemType
Balance Type:	na
Period Type:	duration

- Definition

Public Utilities, Approved Rate Increase (Decrease), Minimum Annual Accrual, Amount

+ References

No definition available.

+ Details

Name:	so_PublicUtilitiesApprovedRateIncreaseDecreaseMinimumAnnualAccrualAmount
Namespace Prefix:	so_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Public Utilities, Customer Refund Payments

+ References

No definition available.

+ Details

Name:	so_PublicUtilitiesCustomerRefundPayments
Namespace Prefix:	so_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Public Utilities, Requested Additional Generating Capacity

+ References

No definition available.

+ Details

Name:	so_PublicUtilitiesRequestedAdditionalGeneratingCapacity
Namespace Prefix:	so_
Data Type:	dtr-types:powerItemType
Balance Type:	na
Period Type:	duration

- Definition

Regulatory Asset, Accrual

+ References

No definition available.

+ Details

Name:	so_RegulatoryAssetAccrual
Namespace Prefix:	so_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Regulatory Clause, Property Damage Reserve

+ References

No definition available.

+ Details

Name:	so_RegulatoryClausePropertyDamageReserve
Namespace Prefix:	so_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 980
-SubTopic 360
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 10.C)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479070/980-360-S99-1

+ 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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 275
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482861/275-10-50-9

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 450
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483076/450-20-50-4

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 450
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483076/450-20-50-9

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 720
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483359/720-20-50-1

Reference 5: http://www.xbrl.org/2003/role/exampleRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 27
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482395/460-10-55-27

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 450
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483076/450-20-50-9

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 450
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483076/450-20-50-4

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482425/460-10-50-3

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 450
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483076/450-20-50-1

+ Details

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

- Definition

The net amount of all regulatory assets less all regulatory liabilities 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/1943274/2147478742/980-340-50-1

+ Details

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

- 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

- Definition

Percentage of public utility's approved rate increase (decrease) by regulatory agency.

+ References

No definition available.

+ Details

Name:	us-gaap_PublicUtilitiesApprovedRateIncreaseDecreasePercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- 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

- Definition

Percentage of public utility's requested rate increase (decrease) with regulatory agency.

+ References

No definition available.

+ Details

Name:	us-gaap_PublicUtilitiesRequestedRateIncreaseDecreasePercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	dei_LegalEntityAxis=so_MississippiPowerMember
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:

- Details

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

- Details

Name:	us-gaap_RegulatoryLiabilityAxis=so_ReliabilityReserveLiabilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PublicUtilitiesRegulatoryProceedingAxis=so_MississippiPSCPEPFilingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PublicUtilitiesRegulatoryProceedingAxis=so_MississippiPSCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PublicUtilitiesRegulatoryProceedingAxis=so_AdValoremTaxAdjustmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PublicUtilitiesRegulatoryProceedingAxis=so_MississippiPSCSRRFilingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PublicUtilitiesRegulatoryProceedingAxis=so_FERCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_RegulatoryLiabilityAxis=so_RegulatoryLiabilityNuclearPTCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Regulatory Matters - MPC (Details) $ in Millions									1 Months Ended		3 Months Ended
Regulatory Matters - MPC (Details) $ in Millions	Aug. 05, 2025 USD ($)	Jul. 30, 2025 USD ($)	Jul. 08, 2025 MW	Jun. 17, 2025 USD ($)	Apr. 03, 2025 USD ($)	Apr. 01, 2025 USD ($)	Mar. 17, 2025 USD ($)	Apr. 11, 2024 USD ($)	Jul. 31, 2025 USD ($)	Apr. 30, 2025 USD ($)	Sep. 30, 2025 USD ($)	Jun. 19, 2025 USD ($)	Jun. 16, 2025 USD ($)
MISSISSIPPI POWER CO
Loss Contingencies [Line Items]
Approved rate increase (decrease)						$ 8.0
MISSISSIPPI POWER CO \| Plant Daniel Units 1 and 2
Loss Contingencies [Line Items]
Proportionate ownership share												50.00%
Proceeds from acquisition		$ 36.0
MISSISSIPPI POWER CO \| Affiliate PPA
Loss Contingencies [Line Items]
Requested additional generating capacity (in MWs) \| MW			50
Approved capacity increase (in MWs) \| MW			750
MISSISSIPPI POWER CO \| Reliability Reserve Liability
Loss Contingencies [Line Items]
Decrease in accrual							$ 10.9
Remaining net book value							$ 57.0
MISSISSIPPI POWER CO \| Mississippi PSC PEP Filing
Loss Contingencies [Line Items]
Requested revenues increase (decrease) percentage				4.00%
Requested rate increase amount				$ 41.0
Approved rate increase, percentage				2.00%
Approved rate increase (decrease)									$ 19.0	$ 22.0
MISSISSIPPI POWER CO \| Mississippi PSC
Loss Contingencies [Line Items]
Approved rate increase (decrease)						$ 6.0
MISSISSIPPI POWER CO \| Ad Valorem Tax Adjustment
Loss Contingencies [Line Items]
Requested rate increase amount	$ 7.0
MISSISSIPPI POWER CO \| Mississippi PSC SRR Filing
Loss Contingencies [Line Items]
Approved rate increase (decrease)				$ 13.5
Minimum annual accrual, amount								$ 12.6
Property damage reserve				$ 125.0									$ 75.0
MISSISSIPPI POWER CO \| FERC
Loss Contingencies [Line Items]
Approved rate increase, percentage					2.50%
Approved rate increase (decrease)					$ 1.0
Customer refund payments					$ 4.0
ALABAMA POWER CO \| Reliability Reserve Liability
Loss Contingencies [Line Items]
Decrease in accrual											$ 30.0
Remaining net book value											101.0	$ 131.0
ALABAMA POWER CO \| Regulatory Liability, Nuclear PTC
Loss Contingencies [Line Items]
Remaining net book value											$ 36.0