Amortization Period For Line Of Credit Facility

No definition available.

Name:	so_AmortizationPeriodForLineOfCreditFacility
Namespace Prefix:	so_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Eligible Project Costs To Be Reimbursed

+ References

No definition available.

+ Details

Name:	so_EligibleProjectCostsToBeReimbursed
Namespace Prefix:	so_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Line of Credit Facility, Conditional Borrowing Commitment

+ References

No definition available.

+ Details

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

- Definition

Percent Of Eligible Project Costs To Be Reimbursed

+ References

No definition available.

+ Details

Name:	so_PercentOfEligibleProjectCostsToBeReimbursed
Namespace Prefix:	so_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
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_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- 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=115995737&loc=d3e659983-123033

+ Details

Name:	us-gaap_JointlyOwnedUtilityPlantProportionateOwnershipShare
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- 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=6877327&loc=d3e13212-122682

+ Details

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

- Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=so_LoanGuaranteeAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_JointlyOwnedUtilityPlantAxis=so_PlantVogtleUnits3And4Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

Financing - DOE Loan Guarantee Borrowings (Details) - USD ($)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2017
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		$ 7,863,000,000
Georgia Power
Debt Instrument [Line Items]
Percent of eligible project costs	70.00%
Eligible project costs to be reimbursed	$ 3,460,000,000
Basis spread on variable rate	0.375%
Line of credit facility, maximum borrowing capacity		1,750,000,000
Amortization period	5 years
Georgia Power \| Loan Guarantee Agreement
Debt Instrument [Line Items]
Credit facility conditional borrowing commitment				$ 1,670,000,000
Plant Vogtle Units 3 And 4 \| Georgia Power
Debt Instrument [Line Items]
Percent ownership	45.70%
FFB Loan \| Georgia Power
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		$ 2,625,000,000.000	$ 2,600,000,000.0