XML 212 R168.htm IDEA: XBRL DOCUMENT
v3.22.0.1

FINANCING - Equity Units (Details) - Junior subordinated notes - USD ($) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2019 | Dec. 31, 2021
Series 2019A and Series 2019B Remarketable Junior Subordinated Notes |  |
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items] |  |
Equity units, per unit issuance price (in dollars per share) | $ 50 |
Equity units, annual distribution rate | 6.75% |
Quarterly interest rate | 2.70% |
Interest rate | 4.05% |
Purchase contract adjustment liability | $ 198,000,000 |
Purchase contract adjustment liability, current |  | $ 52,000,000
Equity units, settlement terms, contract adjustment payments, accretion period | 3 years |
Maximum number of shares (in shares) | 30,200,000 |
Series 2019A Remarketable Junior Subordinated Notes |  |
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items] |  |
Number of shares indexed (in shares) | 34,500,000 |
Equity units, per unit issuance price (in dollars per share) | $ 50 |
Debt face amount | $ 1,725,000,000 |
Proceeds from issuance of mandatory redeemable capital securities | $ 1,682,000,000 |
Equity units, percentage interest in attached debt instrument | 0.0025% |
Series 2019B Remarketable Junior Subordinated Notes |  |
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items] |  |
Equity units, percentage interest in attached debt instrument | 0.0025% |
Anti-Dilution Scenario One | Series 2019A and Series 2019B Remarketable Junior Subordinated Notes |  |
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items] |  |
Equity units, conversion ratio (in shares) | 0.7284 |
Anti-Dilution Scenario One | Minimum | Series 2019A and Series 2019B Remarketable Junior Subordinated Notes |  |
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items] |  |
Equity units, stock price upper threshold (in dollars per share) | $ 68.64 |
Anti-Dilution Scenario Two | Series 2019A and Series 2019B Remarketable Junior Subordinated Notes |  |
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items] |  |
Equity units, per unit issuance price (in dollars per share) | 50 |
Anti-Dilution Scenario Two | Minimum | Series 2019A and Series 2019B Remarketable Junior Subordinated Notes |  |
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items] |  |
Equity units, stock price lower threshold (in dollars per share) | 57.20 |
Anti-Dilution Scenario Two | Maximum | Series 2019A and Series 2019B Remarketable Junior Subordinated Notes |  |
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items] |  |
Equity units, stock price upper threshold (in dollars per share) | $ 68.64 |
Anti-Dilution Scenario Three | Series 2019A and Series 2019B Remarketable Junior Subordinated Notes |  |
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items] |  |
Equity units, conversion ratio (in shares) | 0.8741 |
Anti-Dilution Scenario Three | Maximum | Series 2019A and Series 2019B Remarketable Junior Subordinated Notes |  |
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items] |  |
Equity units, stock price lower threshold (in dollars per share) | $ 57.20 |

X
- Definition Equity Units, Annual Distribution Rate + References No definition available. + Details
Name: | so_EquityUnitsAnnualDistributionRate
Namespace Prefix: | so_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Equity Units, Conversion Ratio, Upper Price Threshold + References No definition available. + Details
Name: | so_EquityUnitsConversionRatioUpperPriceThreshold
Namespace Prefix: | so_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Definition Equity Units, Per Unit Issuance Price + References No definition available. + Details
Name: | so_EquityUnitsPerUnitIssuancePrice
Namespace Prefix: | so_
Data Type: | dtr-types:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition Equity Units, Percentage Interest In Attached Debt Instrument + References No definition available. + Details
Name: | so_EquityUnitsPercentageInterestInAttachedDebtInstrument
Namespace Prefix: | so_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Equity Units, Purchase Contract, Quarterly Adjustment Payment + References No definition available. + Details
Name: | so_EquityUnitsPurchaseContractQuarterlyAdjustmentPayment
Namespace Prefix: | so_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Equity Units, Settlement Terms, Contract Adjustment Payments, Accretion Period + References No definition available. + Details
Name: | so_EquityUnitsSettlementTermsContractAdjustmentPaymentsAccretionPeriod
Namespace Prefix: | so_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Equity Units, Settlement Terms, Maximum Number Of Shares + References No definition available. + Details
Name: | so_EquityUnitsSettlementTermsMaximumNumberOfShares
Namespace Prefix: | so_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Definition Equity Units, Stock Price Lower Threshold + References No definition available. + Details
Name: | so_EquityUnitsStockPriceLowerThreshold
Namespace Prefix: | so_
Data Type: | dtr-types:perShareItemType
Balance Type: | na
Period Type: | instant

X
- Definition Equity Units, Stock Price Upper Threshold + References No definition available. + Details
Name: | so_EquityUnitsStockPriceUpperThreshold
Namespace Prefix: | so_
Data Type: | dtr-types:perShareItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number Of Equity Units Issued + References No definition available. + Details
Name: | so_NumberOfEquityUnitsIssued
Namespace Prefix: | so_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Definition Purchase Contract Adjustment Liability + References No definition available. + Details
Name: | so_PurchaseContractAdjustmentLiability
Namespace Prefix: | so_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Purchase Contract Adjustment Liability, Current + References No definition available. + Details
Name: | so_PurchaseContractAdjustmentLiabilityCurrent
Namespace Prefix: | so_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Face (par) amount of debt instrument at time of issuance. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 1B -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=124435984&loc=d3e28551-108399 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=124429444&loc=SL124452920-239629 Reference 5: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 55 -Paragraph 69C -URI http://asc.fasb.org/extlink&oid=123466577&loc=SL123495737-112612 Reference 6: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 55 -Paragraph 69B -URI http://asc.fasb.org/extlink&oid=123466577&loc=SL123495735-112612 + Details
Name: | us-gaap_DebtInstrumentFaceAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 1B -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
Name: | us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The cash inflow from additional borrowings, net of cash paid to third parties in connection with debt origination. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 14 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3255-108585 + Details
Name: | us-gaap_ProceedsFromDebtNetOfIssuanceCosts
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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_SharesSubjectToMandatoryRedemptionBySettlementTermsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_DebtInstrumentAxis=so_Series2019AAndSeries2019BRemarketableJuniorSubordinatedNotesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=us-gaap_JuniorSubordinatedDebtMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=so_Series2019ARemarketableJuniorSubordinatedNotesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=so_Series2019BRemarketableJuniorSubordinatedNotesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | so_EquityUnitsAntiDilutionScenarioAxis=so_AntiDilutionScenarioOneMember
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: |

X
- Details
Name: | so_EquityUnitsAntiDilutionScenarioAxis=so_AntiDilutionScenarioTwoMember
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: | so_EquityUnitsAntiDilutionScenarioAxis=so_AntiDilutionScenarioThreeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |