PROPERTY, PLANT, AND EQUIPMENT - Ownership and Investment in Jointly-Owned Facilities (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($) mi	Sep. 09, 2021
Alabama Power
Other Ownership Interests [Line Items]
Percent Ownership	14.00%
Alabama Power | Greene County (natural gas) Units 1 and 2
Other Ownership Interests [Line Items]
Percent Ownership	60.00%
Plant in Service	$ 191
Accumulated Depreciation	79
CWIP	$ 1
Alabama Power | Plant Miller (coal) Units 1 and 2
Other Ownership Interests [Line Items]
Percent Ownership	91.80%
Plant in Service	$ 2,133
Accumulated Depreciation	665
CWIP	$ 15
Georgia Power | Plant Hatch (nuclear)
Other Ownership Interests [Line Items]
Percent Ownership	50.10%
Plant in Service	$ 1,382
Accumulated Depreciation	647
CWIP	$ 42
Georgia Power | Plant Vogtle (nuclear) Units 1 and 2
Other Ownership Interests [Line Items]
Percent Ownership	45.70%
Plant in Service	$ 3,611
Accumulated Depreciation	2,265
CWIP	$ 86
Georgia Power | Plant Scherer (coal) Units 1 and 2
Other Ownership Interests [Line Items]
Percent Ownership	8.40%
Plant in Service	$ 276
Accumulated Depreciation	100
CWIP	$ 1
Georgia Power | Plant Scherer (coal) Unit 3
Other Ownership Interests [Line Items]
Percent Ownership	75.00%
Plant in Service	$ 1,314
Accumulated Depreciation	539
CWIP	$ 8
Georgia Power | Plant Wansley (coal)
Other Ownership Interests [Line Items]
Percent Ownership	53.50%
Plant in Service	$ 1,070
Accumulated Depreciation	472
CWIP	$ 7
Georgia Power | Rocky Mountain (pumped storage)
Other Ownership Interests [Line Items]
Percent Ownership	25.40%
Plant in Service	$ 184
Accumulated Depreciation	148
CWIP	$ 1
Mississippi Power | Greene County (natural gas) Units 1 and 2
Other Ownership Interests [Line Items]
Percent Ownership	40.00%
Plant in Service	$ 124
Accumulated Depreciation	61
CWIP	$ 0
Mississippi Power | Plant Daniel (coal) Units 1 and 2
Other Ownership Interests [Line Items]
Percent Ownership	50.00%
Plant in Service	$ 762
Accumulated Depreciation	237
CWIP	$ 19
Southern Company Gas | Dalton Pipeline (natural gas pipeline)
Other Ownership Interests [Line Items]
Percent Ownership	50.00%
Plant in Service	$ 271
Accumulated Depreciation	19
CWIP	$ 0
Pipeline infrastructure (miles) | mi	115
Agreement to lease undivided ownership (percent)	50.00%
Future minimum payments receivable	$ 26
Plant Daniel | Mississippi Power
Other Ownership Interests [Line Items]
Percent Ownership		50.00%