XML 159 R115.htm IDEA: XBRL DOCUMENT
v3.22.0.1

REGULATORY MATTERS - GPC Rate Plans, Integrated Resource Plan and COVID-19 Costs (Details) $ in Millions |  |  |  |  |  |  |  | 4 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Jan. 01, 2024 MW | Jan. 31, 2022 agreement MW | Jan. 01, 2022 USD ($) | Nov. 18, 2021 USD ($) | Nov. 02, 2021 USD ($) | Jun. 15, 2021 USD ($) | Jan. 01, 2021 USD ($) | Sep. 30, 2020 USD ($) | Dec. 31, 2035 MW | Dec. 31, 2030 MW | Dec. 31, 2029 MW | Dec. 31, 2028 MW | Dec. 31, 2026 MW | Dec. 31, 2025 MW | Dec. 31, 2024 MW | Dec. 31, 2021 USD ($) MW | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2013
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net regulatory assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 4,711.0 | $ 5,493.0 |  |  |
Customer Refunds |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net regulatory assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (189.0) | $ (56.0) |  |  |
Georgia Power |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Approved rate increase |  |  |  |  |  |  | $ 90.0 |  |  |  |  |  |  |  |  |  |  |  |  |
Approved rate decrease |  |  |  |  |  |  | $ 10.0 |  |  |  |  |  |  |  |  |  |  |  |  |
Retail rate of return on common equity |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10.50% |  | 10.95%
Portion of actual earnings above approved ROE band applied to reduce regulatory assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 40.00% |  |
Portion of actual earnings above approved ROE band retained by subsidiary company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 20.00% |  |
Portion of actual earnings above approved ROE band refunded to customers |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 50.00% | 40.00% |  | 66.67%
Customer refund liability in absence of base rate case |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 5.0 |  | $ 110.0 |  |
Portion of actual earnings above approved ROE band refunded to customers, value |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 50.0 | $ 60.0 |  |
Portion of actual earnings above approved ROE band retained by Georgia Power |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 33.33%
Portion of actual earnings above approved ROE band refunded to customers, used to reduce regulatory assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 50.00% | 50.00% |  |
Portion of actual earning above approved ROE band refunded to customers, used to reduce regulatory assets, value |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 60.0 |  | $ 50.0 |
Public utilities, approved rate increase (decrease), amount |  |  |  | $ 252.0 |  |  |  | $ (44.0) |  |  |  |  |  |  |  |  |  |  |  |
Requested additional generating capacity (in MW) | MW |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 970 |  |  |  |
Approved additional generating capacity (in MW) | MW |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 970 |  |  |  |
Incremental COVID-19 costs deferred |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 21.0 | 38.0 |  |  |
Incremental COVID-19 costs deferred, bad debt costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 23.0 |  |  |
Incremental COVID-19 costs deferred, other |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 15.0 |  |  |
Net regulatory assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3,928.0 | 4,252.0 |  |  |
Georgia Power | Plant Vogtle Unit 3 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public utilities, approved rate increase (decrease), amount |  |  |  |  | $ 2,100.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested rate increase (decrease), amount |  |  |  |  | 3,600.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Approved depreciation expense deferred, annual amount |  |  |  |  | $ 38.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested rate increase, annual amount |  |  |  |  |  | $ 302.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Georgia Power | Plant Wansley Units 1 and 2 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net regulatory assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 610.0 |  |  |  |
Georgia Power | Plant Bowen Units 1 and 2 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net regulatory assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 937.0 |  |  |  |
Georgia Power | Plant Scherer Unit 3 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net regulatory assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 622.0 |  |  |  |
Georgia Power | Subsequent Event |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested additional generating capacity (in MW) | MW |  |  |  |  |  |  |  |  | 3,700 |  |  |  |  |  |  |  |  |  |  |
Requested number of power purchase agreements to be certified | agreement |  | 6 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested number of affiliate power purchase agreements to be certified | agreement |  | 5 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Georgia Power | Subsequent Event | Scenario, Forecast |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested additional generating capacity (in MW) | MW | 1,567 |  |  |  |  |  |  |  |  | 1,000 | 2,300 | 228 | 265 | 380 | 88 |  |  |  |  |
Georgia Power | Subsequent Event | Plant Vogtle Unit 3 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Decrease in tariff |  |  | $ 78.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Georgia Power | Subsequent Event | Plant Wansley Units 1 and 2 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Capacity of units included in request for decertification of units | MW |  | 926 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Request for decertification of units, percentage of ownership |  | 53.50% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Georgia Power | Subsequent Event | Plant Bowen Units 1 and 2 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Capacity of units included in request for decertification of units | MW |  | 1,400 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Georgia Power | Subsequent Event | Plant Scherer Unit 3 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Capacity of units included in request for decertification of units | MW |  | 614 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Request for decertification of units, percentage of ownership |  | 75.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Georgia Power | Subsequent Event | Plant Gaston Units 1 through 4 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Capacity of units included in request for decertification of units | MW |  | 500 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Request for decertification of units, percentage of ownership |  | 50.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Georgia Power | Subsequent Event | Plant Bowen Units 3 and 4 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested additional generating capacity (in MW) | MW |  | 1,760 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Georgia Power | Subsequent Event | Plant Scherer Units 1 and 2 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested additional generating capacity (in MW) | MW |  | 137 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percent ownership |  | 8.40% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Georgia Power | Subsequent Event | Plant Sinclair |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested additional generating capacity (in MW) | MW |  | 45 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Georgia Power | Subsequent Event | Plant North Highlands |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested additional generating capacity (in MW) | MW |  | 30 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Georgia Power | Subsequent Event | Plant Burton |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested additional generating capacity (in MW) | MW |  | 6 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Georgia Power | Customer Refunds |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Portion of actual earnings above approved ROE band refunded to customers, value |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5.0 |  | $ 110.0 |  |
Net regulatory assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (8.0) | (6.0) |  |  |
Remaining Net Book Value of Retired Assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net regulatory assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,050.0 | 1,183.0 |  |  |
Remaining Net Book Value of Retired Assets | Georgia Power |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net regulatory assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 455.0 | $ 527.0 |  |  |
Maximum | Georgia Power |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Retail rate of return on common equity |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 12.00% |  | 12.00%
Maximum | Remaining Net Book Value of Retired Assets | Georgia Power |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory asset amortization period |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3 years |  |
Minimum | Georgia Power |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Retail rate of return on common equity |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 9.50% |  | 10.00%

X
- Definition Capacity Of Units Included In request for decertify coal and oil-fired plants. + References No definition available. + Details
Name: | so_CapacityOfUnitsIncludedInRequestForDecertificationOfUnits
Namespace Prefix: | so_
Data Type: | dtr-types:powerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Customer Refund Liability in Absence of Base Rate Case + References No definition available. + Details
Name: | so_CustomerRefundLiabilityinAbsenceofBaseRateCase
Namespace Prefix: | so_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Increase (Decrease) In Tariff + References No definition available. + Details
Name: | so_IncreaseDecreaseInTariff
Namespace Prefix: | so_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Portion Of Actual Earnings Above Approved ROE Band Applied To Reduce Regulatory Assets + References No definition available. + Details
Name: | so_PortionOfActualEarningsAboveApprovedROEBandAppliedToReduceRegulatoryAssets
Namespace Prefix: | so_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Portion Of Actual Earnings Above Approved ROE Band Refunded To Customers, Used To Reduce Regulatory Assets, Percent + References No definition available. + Details
Name: | so_PortionOfActualEarningsAboveApprovedROEBandRefundedToCustomersUsedToReduceRegulatoryAssetsPercent
Namespace Prefix: | so_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Portion Of Actual Earnings Above Approved ROE Band Refunded To Customers, Used To Reduce Regulatory Assets, Value + References No definition available. + Details
Name: | so_PortionOfActualEarningsAboveApprovedROEBandRefundedToCustomersUsedToReduceRegulatoryAssetsValue
Namespace Prefix: | so_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Portion Of Actual Earnings Above Approved ROE Band Refunded To Customers, Value + References No definition available. + Details
Name: | so_PortionOfActualEarningsAboveApprovedROEBandRefundedToCustomersValue
Namespace Prefix: | so_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Portion Of Actual Earnings Above Approved ROE Band Retained + References No definition available. + Details
Name: | so_PortionOfActualEarningsAboveApprovedROEBandRetained
Namespace Prefix: | so_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Portion of actual earnings above approved ROE band refunded to customers. + References No definition available. + Details
Name: | so_PortionOfActualEarningsAboveApprovedRoeBandRefundedToCustomers
Namespace Prefix: | so_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Portion of actual earnings above approved ROE band retained by subsidiary company. + References No definition available. + Details
Name: | so_PortionOfActualEarningsAboveApprovedRoeBandRetainedBySubsidiaryCompany
Namespace Prefix: | so_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- 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

X
- Definition Public Utilities, Approved Depreciation Expense Deferred, Annual Amount + References No definition available. + Details
Name: | so_PublicUtilitiesApprovedDepreciationExpenseDeferredAnnualAmount
Namespace Prefix: | so_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Public Utilities, Approved Rate Decrease, Amount + References No definition available. + Details
Name: | so_PublicUtilitiesApprovedRateDecreaseAmount
Namespace Prefix: | so_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Public Utilities, Approved Rate Increase, Amount + References No definition available. + Details
Name: | so_PublicUtilitiesApprovedRateIncreaseAmount
Namespace Prefix: | so_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Public Utilities, Incremental COVID-19 Costs Deferred + References No definition available. + Details
Name: | so_PublicUtilitiesIncrementalCOVID19CostsDeferred
Namespace Prefix: | so_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Public Utilities, Incremental COVID-19 Costs Deferred, Credit Loss, Expense + References No definition available. + Details
Name: | so_PublicUtilitiesIncrementalCOVID19CostsDeferredCreditLossExpense
Namespace Prefix: | so_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Public Utilities, Incremental COVID-19 Costs Deferred, Other + References No definition available. + Details
Name: | so_PublicUtilitiesIncrementalCOVID19CostsDeferredOther
Namespace Prefix: | so_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- 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

X
- Definition Public Utilities, Requested Number of Affiliate Power Purchase Agreements to be Certified + References No definition available. + Details
Name: | so_PublicUtilitiesRequestedNumberOfAffiliatePowerPurchaseAgreementsToBeCertified
Namespace Prefix: | so_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Public Utilities, Requested Number of Power Purchase Agreements to be Certified, Total + References No definition available. + Details
Name: | so_PublicUtilitiesRequestedNumberOfPowerPurchaseAgreementsToBeCertifiedTotal
Namespace Prefix: | so_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Public Utilities, Requested Rate Increase (Decrease), Annual Amount + References No definition available. + Details
Name: | so_PublicUtilitiesRequestedRateIncreaseDecreaseAnnualAmount
Namespace Prefix: | so_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Request For Decertification Of Units, Percentage of Ownership + References No definition available. + Details
Name: | so_RequestForDecertificationOfUnitsPercentageOfOwnership
Namespace Prefix: | so_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Retail Rate Of Return On Common Equity + References No definition available. + Details
Name: | so_RetailRateOfReturnOnCommonEquity
Namespace Prefix: | so_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The proportionate share of interest (percent) in a jointly owned utility plant. + 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 http://asc.fasb.org/extlink&oid=122136288&loc=d3e659983-123033 + Details
Name: | us-gaap_JointlyOwnedUtilityPlantProportionateOwnershipShare
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- 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 -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382 + Details
Name: | us-gaap_NetRegulatoryAssets
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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 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
- 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: | duration

X
- Details
Name: | us-gaap_RegulatoryLiabilityAxis=so_CustomerRefundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | us-gaap_PublicUtilityAxis=so_PlantVogtleUnit3Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PublicUtilityAxis=so_PlantWansleyUnits1And2Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PublicUtilityAxis=so_PlantBowenUnits1And2Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PublicUtilityAxis=so_PlantSchererUnit3Member
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: | srt_StatementScenarioAxis=srt_ScenarioForecastMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PublicUtilityAxis=so_PlantGastonUnits1Through4Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PublicUtilityAxis=so_PlantBowenUnits3And4Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PublicUtilityAxis=so_PlantSchererUnits1And2Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PublicUtilityAxis=so_PlantSinclairMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PublicUtilityAxis=so_PlantNorthHighlandsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PublicUtilityAxis=so_PlantBurtonMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RegulatoryAssetAxis=so_RemainingNetBookValueOfRetiredAssetsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |