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Derivatives - Schedule of Cumulative Basis Adjustments for Fair Value Hedges (Details) - Fair Value Hedging - Long-term debt - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Derivative [Line Items]
Carrying Amount of the Hedged Item	$ (3,733)	$ (2,936)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	164	242
SOUTHERN Co GAS
Derivative [Line Items]
Carrying Amount of the Hedged Item	(445)	(422)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	$ 52	$ 75

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- Definition

Derivative, Cumulative Amount of Fair Value Hedging Adjustment Included in Carrying Amount

+ References

No definition available.

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- Definition

Amount of hedged item in hedging relationship. Excludes hedged asset or liability.

+ References

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- 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

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 20
-Name Accounting Standards Codification
-Section 25
-Paragraph 6A
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480682/815-20-25-6A

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480237/815-40-50-5

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