Performance Evaluation Plan, Measurement Input

No definition available.

Name:	so_PerformanceEvaluationPlanMeasurementInput
Namespace Prefix:	so_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

Performance Evaluation Plan, Number Of Filings Per Calendar Year

+ References

No definition available.

+ Details

Name:	so_PerformanceEvaluationPlanNumberOfFilingsPerCalendarYear
Namespace Prefix:	so_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- 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

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

- Definition

Amortization period for the recovery of regulatory asset, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_RegulatoryAssetAmortizationPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Details

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

- Details

Name:	srt_RangeAxis=srt_WeightedAverageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MeasurementInputTypeAxis=so_MeasurementInputAverageCustomerPriceMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MeasurementInputTypeAxis=so_MeasurementInputServiceReliabilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MeasurementInputTypeAxis=so_MeasurementInputCustomerSatisfactionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

REGULATORY MATTERS - MPC 2019 Base Rate Case and Performance Evaluation Plan (Details) $ in Millions	1 Months Ended				12 Months Ended
	Jun. 30, 2023 USD ($)	Jun. 30, 2022 USD ($)	Jun. 30, 2021 USD ($)	May 31, 2021 USD ($)	Dec. 31, 2023 filing	Dec. 31, 2021 USD ($)
Public Utilities, General Disclosures [Line Items]
Regulatory asset amortization period					4 years
Mississippi Power
Public Utilities, General Disclosures [Line Items]
Public utilities, approved rate increase (decrease), amount \| $	$ (7)	$ 18	$ 16	$ 28		$ 9
Approved rate decrease, percent		(1.90%)	(1.80%)
Performance evaluation plan, number of filings per calendar year \| filing					2
Mississippi Power \| Weighted Average \| Measurement Input, Average Customer Price
Public Utilities, General Disclosures [Line Items]
Performance evaluation plan, measurement input					0.40
Mississippi Power \| Weighted Average \| Measurement Input, Service Reliability
Public Utilities, General Disclosures [Line Items]
Performance evaluation plan, measurement input					0.40
Mississippi Power \| Weighted Average \| Measurement Input, Customer Satisfaction
Public Utilities, General Disclosures [Line Items]
Performance evaluation plan, measurement input					0.20