INCOME TAXES - Narrative (Details) - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Dec. 31, 2021	Dec. 31, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Line Items]
Deferred income tax assets	$ 8,914	$ 8,914	$ 8,914	$ 8,874
ITC and PTC carryforward
Income Tax Disclosure [Line Items]
Deferred income tax assets	1,750	1,750	1,750	1,853
Southern Power
Income Tax Disclosure [Line Items]
Deferred income tax assets	1,258	1,258	$ 1,258	1,587
Percentage reduction in tax basis of assets			50.00%
Southern Power | ITCs and other credits carryforward
Income Tax Disclosure [Line Items]
Reduction in income tax expense, investment tax credits			$ 289	340	$ 734
Southern Power | ITC and PTC carryforward
Income Tax Disclosure [Line Items]
Deferred income tax assets	827	827	827	1,110
Southern Power | ITC and PTC carryforward | Nacogdoches Biomass Generating Plant
Income Tax Disclosure [Line Items]
Reduction in income tax expense, investment tax credits					5
Southern Power | Production Tax Credit Carryforward
Income Tax Disclosure [Line Items]
Effective income tax rate reconciliation, tax credit, production, amount			16	15	12
Georgia Power
Income Tax Disclosure [Line Items]
Deferred income tax assets	4,019	4,019	4,019	3,443
State investment tax credit carryforward			428
Georgia Power | ITC and PTC carryforward
Income Tax Disclosure [Line Items]
Deferred income tax assets	704	704	704	539
Mississippi Power
Income Tax Disclosure [Line Items]
Deferred income tax assets	393	393	393	428
Mississippi Power | ITC and PTC carryforward
Income Tax Disclosure [Line Items]
Deferred income tax assets	0	0	0	0
Southern Company Gas
Income Tax Disclosure [Line Items]
Deferred income tax assets	328	328	328	432
Southern Company Gas | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Sequent
Income Tax Disclosure [Line Items]
Deferred tax expense, increase from change in appointment rate	85	85	85
Southern Company Gas | ITC and PTC carryforward
Income Tax Disclosure [Line Items]
Deferred income tax assets	0	0	0	0
State and Local Jurisdiction | Georgia Power
Income Tax Disclosure [Line Items]
Valuation allowance	58	58	58
State and Local Jurisdiction | Georgia Power | ITCs and other credits carryforward
Income Tax Disclosure [Line Items]
Reduction in income tax expense, investment tax credits			66	67	51
State and Local Jurisdiction | Southern Company Gas
Income Tax Disclosure [Line Items]
Valuation allowance					5
Deferred Charges Related To Income Taxes, Current | Other Noncurrent Assets | Southern Power | Unrealized Tax Credits
Income Tax Disclosure [Line Items]
Deferred income tax assets	6	6	6	$ 5	$ 51
Mississippi | State and Local Jurisdiction | Mississippi Power
Income Tax Disclosure [Line Items]
Operating loss carryforwards, valuation allowance	32	32	32
New York | State and Local Jurisdiction | Southern Power
Income Tax Disclosure [Line Items]
Operating loss carryforwards, valuation allowance	25	25	25
Oklahoma | State and Local Jurisdiction | Southern Power
Income Tax Disclosure [Line Items]
Operating loss carryforwards, valuation allowance	11	11	11
Florida | State and Local Jurisdiction | Southern Power
Income Tax Disclosure [Line Items]
Operating loss carryforwards, valuation allowance	$ 10	$ 10	$ 10