Bank credit arrangements no term loan due with in one year.

No definition available.

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

- Definition

Line Of Credit Expire Year Five

+ References

No definition available.

+ Details

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

- Definition

Line Of Credit Expire Year One

+ References

No definition available.

+ Details

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

- Definition

Line Of Credit Expire Year Three

+ References

No definition available.

+ Details

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

- Definition

Line Of Credit Expire Year Two

+ References

No definition available.

+ Details

Name:	so_LineOfCreditExpireYearTwo
Namespace Prefix:	so_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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

No definition available.

+ Details

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

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	dei_LegalEntityAxis=so_SouthernCompanyMember
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:	dei_LegalEntityAxis=so_GeorgiaPowerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	us-gaap_CreditFacilityAxis=so_ContinuingLetterOfCreditFacilityAMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=so_ContinuingLetterOfCreditFacilityBMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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

- Details

Name:	dei_LegalEntityAxis=so_NicorGasMember
Namespace Prefix:
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Period Type:

Financing - Schedule of Credit Arrangements (Details) - USD ($)	Sep. 30, 2021	Aug. 31, 2021	Jul. 31, 2021	May 31, 2021	Apr. 30, 2021
Line of Credit Facility [Line Items]
Expires, 2022	$ 280,000,000
Expires, 2023	125,000,000
Expires, 2024	700,000,000
Expires, 2026	6,550,000,000
Total	7,655,000,000
Unused	7,570,000,000
Due within One Year	280,000,000
Southern Company parent
Line of Credit Facility [Line Items]
Expires, 2022	0
Expires, 2023	0
Expires, 2024	0
Expires, 2026	2,000,000,000
Total	2,000,000,000
Unused	1,999,000,000
Due within One Year	0
ALABAMA POWER CO
Line of Credit Facility [Line Items]
Expires, 2022	0		$ 525,000,000
Expires, 2023	0
Expires, 2024	550,000,000	$ 550,000,000
Expires, 2026	700,000,000
Total	1,250,000,000			$ 700,000,000	$ 800,000,000
Unused	1,250,000,000
Due within One Year	0
GEORGIA POWER CO
Line of Credit Facility [Line Items]
Expires, 2022	0
Expires, 2023	0
Expires, 2024	0
Expires, 2026	1,750,000,000
Total	1,750,000,000
Unused	1,726,000,000
Due within One Year	0
MISSISSIPPI POWER CO
Line of Credit Facility [Line Items]
Expires, 2022	0
Expires, 2023	125,000,000
Expires, 2024	150,000,000
Expires, 2026	0
Total	275,000,000			150,000,000
Unused	250,000,000
Due within One Year	0
SOUTHERN POWER CO
Line of Credit Facility [Line Items]
Expires, 2022	0
Expires, 2023	0
Expires, 2024	0
Expires, 2026	600,000,000
Total	600,000,000
Unused	568,000,000
Due within One Year	0
SOUTHERN POWER CO \| Continuing Letter of Credit Facility A
Line of Credit Facility [Line Items]
Expires, 2023	75,000,000
Unused	23,000,000
SOUTHERN POWER CO \| Continuing Letter of Credit Facility B
Line of Credit Facility [Line Items]
Expires, 2023	60,000,000
Unused	1,000,000
SOUTHERN Co GAS
Line of Credit Facility [Line Items]
Expires, 2022	250,000,000
Expires, 2023	0
Expires, 2024	0
Expires, 2026	1,500,000,000
Total	1,750,000,000			$ 1,500,000,000	$ 1,750,000,000
Unused	1,747,000,000
Due within One Year	250,000,000
SEGCO
Line of Credit Facility [Line Items]
Expires, 2022	30,000,000
Expires, 2023	0
Expires, 2024	0
Expires, 2026	0
Total	30,000,000
Unused	30,000,000
Due within One Year	30,000,000
Southern Company Gas Capital
Line of Credit Facility [Line Items]
Total	800,000,000
Nicor Gas
Line of Credit Facility [Line Items]
Total	$ 700,000,000