XML 139 R95.htm IDEA: XBRL DOCUMENT
v3.22.0.1

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Average AFUDC Composite Rates (Details) | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | --- | ---
Alabama Power |  |  |
Capitalized Contract Cost [Line Items] |  |  |
Composite rate | 7.90% | 8.10% | 8.40%
Georgia Power |  |  |
Capitalized Contract Cost [Line Items] |  |  |
Composite rate | 7.20% | 6.90% | 6.90%
Mississippi Power |  |  |
Capitalized Contract Cost [Line Items] |  |  |
Composite rate | 2.50% | 5.40% | 7.30%
Atlanta Gas Light |  |  |
Capitalized Contract Cost [Line Items] |  |  |
Composite rate | 7.70% | 7.70% | 7.80%
Chattanooga Gas |  |  |
Capitalized Contract Cost [Line Items] |  |  |
Composite rate | 7.10% | 7.10% | 7.10%
Nicor Gas |  |  |
Capitalized Contract Cost [Line Items] |  |  |
Composite rate | 0.10% | 0.70% | 2.30%

X
- Definition Composite Rate Used For Allowance For Funds Used During Construction + References No definition available. + Details
Name: | so_CompositeRateUsedForAllowanceForFundsUsedDuringConstruction
Namespace Prefix: | so_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

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

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

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

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

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