Disposal Group, Including Discontinued Operation, Number Of Distribution Utilities

No definition available.

Name:	so_DisposalGroupIncludingDiscontinuedOperationNumberOfDistributionUtilities
Namespace Prefix:	so_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Natural Gas Revenues

+ References

No definition available.

+ Details

Name:	so_NaturalGasRevenues
Namespace Prefix:	so_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfReportableSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of states the entity operates in as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfStatesInWhichEntityOperates
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount, including tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value-added and excise.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130539-203045

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130545-203045

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130543-203045

+ Details

Name:	us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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_SegmentReportingInformationLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

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

- Details

Name:	srt_CounterpartyNameAxis=so_TraditionalElectricOperatingCompaniesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=so_SouthernCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DisposalGroupClassificationAxis=us-gaap_DisposalGroupDisposedOfBySaleNotDiscontinuedOperationsMember
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:	srt_ProductOrServiceAxis=so_WholesaleAffiliatesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Segment and Related Information - Narrative (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) state	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) state segment	Sep. 30, 2017 USD ($)	Jul. 31, 2018 utility
Segment Reporting Information [Line Items]
Number of reportable segments \| segment			4
Number of states in which entity operates \| state	4		4
Total operating revenues	$ 6,159	$ 6,201	$ 18,158	$ 17,403
SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Number of reportable segments \| segment			4
Number of states in which entity operates \| state	7		7
Total operating revenues	$ 492	565	$ 2,861	2,841
SOUTHERN Co GAS \| Traditional Electric Operating Companies
Segment Reporting Information [Line Items]
Natural gas revenues	14	9	22	19
SOUTHERN Co GAS \| Southern Company
Segment Reporting Information [Line Items]
Natural gas revenues	38	38	96	94
SOUTHERN Co GAS \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Segment Reporting Information [Line Items]
Number of natural gas distribution utilities disposed \| utility					3
SOUTHERN POWER CO
Segment Reporting Information [Line Items]
Total operating revenues	635	618	1,699	1,597
SOUTHERN POWER CO \| Wholesale revenues, affiliates
Segment Reporting Information [Line Items]
Total operating revenues	$ 134	$ 105	$ 326	$ 295