ASSET RETIREMENT OBLIGATIONS - Estimated Costs of Decommissioning (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)
Alabama Power | Plant Farley
Public Utilities, General Disclosures [Line Items]
Decommissioning periods: Beginning year	2037
Decommissioning periods: Completion year	2076
Site study costs	$ 1,720
Alabama Power | Radiated structures | Plant Farley
Public Utilities, General Disclosures [Line Items]
Site study costs	1,234
Alabama Power | Spent fuel management | Plant Farley
Public Utilities, General Disclosures [Line Items]
Site study costs	387
Alabama Power | Non-radiated structures | Plant Farley
Public Utilities, General Disclosures [Line Items]
Site study costs	$ 99
Georgia Power | Plant Hatch
Public Utilities, General Disclosures [Line Items]
Decommissioning periods: Beginning year	2034
Decommissioning periods: Completion year	2075
Site study costs	$ 962
Georgia Power | Plant Vogtle Units 1 and 2
Public Utilities, General Disclosures [Line Items]
Decommissioning periods: Beginning year	2047
Decommissioning periods: Completion year	2079
Site study costs	$ 842
Georgia Power | Radiated structures | Plant Hatch
Public Utilities, General Disclosures [Line Items]
Site study costs	734
Georgia Power | Radiated structures | Plant Vogtle Units 1 and 2
Public Utilities, General Disclosures [Line Items]
Site study costs	601
Georgia Power | Spent fuel management | Plant Hatch
Public Utilities, General Disclosures [Line Items]
Site study costs	172
Georgia Power | Spent fuel management | Plant Vogtle Units 1 and 2
Public Utilities, General Disclosures [Line Items]
Site study costs	162
Georgia Power | Non-radiated structures | Plant Hatch
Public Utilities, General Disclosures [Line Items]
Site study costs	56
Georgia Power | Non-radiated structures | Plant Vogtle Units 1 and 2
Public Utilities, General Disclosures [Line Items]
Site study costs	$ 79