INCOME TAXES - Reconciliation of Federal Statutory Income Tax Rate (Details)	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Reconciliation of federal statutory income tax rate to effective income tax rate
Federal statutory rate	21.00%	21.00%	21.00%
State income tax, net of federal deduction	5.50%	2.80%	4.90%
Employee stock plans' dividend deduction	(0.90%)	(0.70%)	(0.40%)
Non-deductible book depreciation	0.90%	0.70%	0.30%
Flowback of excess deferred income taxes	(11.70%)	(8.80%)	(2.10%)
AFUDC-Equity	(1.50%)	(0.80%)	(0.40%)
ITC basis difference			(0.10%)
Federal PTCs	0.00%	0.00%
Amortization of ITC	(2.20%)	(1.60%)	(0.80%)
Tax impact from sale of subsidiaries			5.10%
Noncontrolling interests	0.80%	0.00%	0.00%
Leveraged lease impairments and dispositions	(1.40%)	(1.60%)
Other	(0.10%)	0.20%	0.00%
Effective income tax (benefit) rate	10.40%	11.20%	27.50%
Alabama Power
Reconciliation of federal statutory income tax rate to effective income tax rate
Federal statutory rate	21.00%	21.00%	21.00%
State income tax, net of federal deduction	4.60%	5.00%	4.90%
Employee stock plans' dividend deduction	0.00%	0.00%	0.00%
Non-deductible book depreciation	0.50%	0.60%	0.60%
Flowback of excess deferred income taxes	(2.60%)	(3.10%)	(5.30%)
AFUDC-Equity	(0.70%)	(0.60%)	(0.80%)
ITC basis difference			0.00%
Federal PTCs	0.00%	0.00%
Amortization of ITC	(0.10%)	(0.10%)	(0.10%)
Tax impact from sale of subsidiaries			0.00%
Noncontrolling interests	0.00%	0.00%	0.00%
Leveraged lease impairments and dispositions	0.00%	0.00%
Other	0.20%	(0.30%)	(0.40%)
Effective income tax (benefit) rate	22.90%	22.50%	19.90%
Georgia Power
Reconciliation of federal statutory income tax rate to effective income tax rate
Federal statutory rate	21.00%	21.00%	21.00%
State income tax, net of federal deduction	(5.70%)	0.50%	1.00%
Employee stock plans' dividend deduction	0.00%	0.00%	0.00%
Non-deductible book depreciation	3.10%	0.80%	0.50%
Flowback of excess deferred income taxes	(49.90%)	(12.00%)	0.00%
AFUDC-Equity	(6.40%)	(1.10%)	(0.60%)
ITC basis difference			0.00%
Federal PTCs	0.00%	0.00%
Amortization of ITC	(0.40%)	(0.10%)	(0.10%)
Tax impact from sale of subsidiaries			0.00%
Noncontrolling interests	0.00%	0.00%	0.00%
Leveraged lease impairments and dispositions	0.00%	0.00%
Other	(1.90%)	(0.30%)	(0.30%)
Effective income tax (benefit) rate	(40.20%)	8.80%	21.50%
Mississippi Power
Reconciliation of federal statutory income tax rate to effective income tax rate
Federal statutory rate	21.00%	21.00%	21.00%
State income tax, net of federal deduction	4.90%	4.80%	4.30%
Employee stock plans' dividend deduction	0.00%	0.00%	0.00%
Non-deductible book depreciation	0.40%	0.50%	0.40%
Flowback of excess deferred income taxes	(15.20%)	(18.50%)	(12.60%)
AFUDC-Equity	0.00%	(0.10%)	(0.10%)
ITC basis difference			0.00%
Federal PTCs	0.00%	0.00%
Amortization of ITC	0.00%	(0.10%)	(0.10%)
Tax impact from sale of subsidiaries			0.00%
Noncontrolling interests	0.00%	0.00%	0.00%
Leveraged lease impairments and dispositions	0.00%	0.00%
Other	0.60%	0.90%	4.90%
Effective income tax (benefit) rate	11.70%	8.50%	17.80%
Southern Power
Reconciliation of federal statutory income tax rate to effective income tax rate
Federal statutory rate	21.00%	21.00%	21.00%
State income tax, net of federal deduction	(8.00%)	2.70%	4.00%
Employee stock plans' dividend deduction	0.00%	0.00%	0.00%
Non-deductible book depreciation	0.00%	0.00%	0.00%
Flowback of excess deferred income taxes	0.00%	0.00%	0.00%
AFUDC-Equity	0.00%	0.00%	0.00%
ITC basis difference			(1.90%)
Federal PTCs	(4.60%)	(2.50%)
Amortization of ITC	(29.70%)	(22.10%)	(16.10%)
Tax impact from sale of subsidiaries			(27.60%)
Noncontrolling interests	13.40%	3.10%	0.80%
Leveraged lease impairments and dispositions	0.00%	0.00%
Other	(0.40%)	(0.90%)	(0.60%)
Effective income tax (benefit) rate	(8.30%)	1.30%	(20.40%)
Southern Company Gas
Reconciliation of federal statutory income tax rate to effective income tax rate
Federal statutory rate	21.00%	21.00%	21.00%
State income tax, net of federal deduction	15.10%	4.00%	6.10%
Employee stock plans' dividend deduction	0.00%	0.00%	0.00%
Non-deductible book depreciation	0.00%	0.00%	0.00%
Flowback of excess deferred income taxes	(2.80%)	(2.70%)	(6.00%)
AFUDC-Equity	0.00%	0.00%	0.00%
ITC basis difference			0.00%
Federal PTCs	0.00%	0.00%
Amortization of ITC	(0.10%)	(0.10%)	(0.10%)
Tax impact from sale of subsidiaries			(1.40%)
Noncontrolling interests	0.00%	0.00%	0.00%
Leveraged lease impairments and dispositions	0.00%	0.00%
Other	0.60%	0.50%	(1.40%)
Effective income tax (benefit) rate	33.80%	22.70%	18.20%

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Effective Income Tax Rate Reconciliation Amortization Tax Credits Investment

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Effective Income Tax Rate Reconciliation, Tax Credit, Production, Percent

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to deduction for dividend paid to employee stock ownership plan.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to disposition of a business not qualifying as a discontinued operation.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to noncontrolling interest income (loss) exempt from income taxes.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to revisions of previously reported income tax expense.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to state and local income tax expense (benefit), net of federal tax expense (benefit).

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