Consolidated Statements of Comprehensive Income - GAS (Parenthetical) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Qualifying hedges, change in fair value, tax	$ (17)	$ (19)	$ (16)
Qualifying hedges, reclassification adjustment, tax	27	23	31
Pension and other postretirement benefit plans, gain (loss), tax	(14)	18	37
Reclassification adjustment for amounts included in net income, tax	0	3	5
Southern Company Gas
Qualifying hedges, change in fair value, tax	(18)	5	5
Qualifying hedges, reclassification adjustment, tax	19	(9)	(5)
Pension and other postretirement benefit plans, gain (loss), tax	(7)	8	17
Reclassification adjustment for amounts included in net income, tax	$ 0	$ 0	$ 0

Amount of tax expense (benefit) for (increase) decrease in value of benefit obligation for change in actuarial assumptions and increase (decrease) in value of plan assets from experience different from that assumed of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 12
-SubTopic 10
-Topic 220
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482790/220-10-45-12

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- Definition

Amount, before reclassification, of tax expense (benefit) for gain (loss) from derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 12
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482790/220-10-45-12

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Amount of tax expense (benefit) for reclassification of gain (loss) from accumulated other comprehensive income (AOCI) for derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

+ References

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Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan.

+ References

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