CONTINGENCIES, COMMITMENTS, AND GUARANTEES - Nuclear Fuel Disposal Costs and Nuclear Insurance (Details)	12 Months Ended	108 Months Ended
	Dec. 31, 2020 USD ($) plant	Dec. 31, 2019 USD ($)
Jointly Owned Utility Plant Interests [Line Items]
Maximum fund for public liability claims arising from a single nuclear incident under price - anderson amendments act	$ 13,800,000,000
Maximum insurance coverage provided by American Nuclear Insurers to each nuclear plant	450,000,000
Maximum amount that a company could be assessed per incident for each licensed reactor	138,000,000
Maximum aggregate amount that a reactor can assess in a calendar period for each incident	$ 20,000,000
Block period considered for inflation adjustment against maximum assessment per reactor	5 years
Maximum deductible waiting period	182 days
Maximum coverage per occurrence per unit limit to obtain replacement power	$ 490,000,000
Aggregate payment for claims resulting from terrorist acts in one year period	3,200,000,000
Vogtle Units 3 and 4
Jointly Owned Utility Plant Interests [Line Items]
Maximum limits for accidental property damage occurring during construction	$ 2,750,000,000
Alabama Power and Georgia Power
Jointly Owned Utility Plant Interests [Line Items]
Number of nuclear fuel plants | plant	3
Maximum property damage insurance provided to nuclear generating facilities	$ 1,500,000,000
Maximum additional coverage provided for losses under excess insurance	1,250,000,000
Maximum additional coverage provided for losses under excess insurance, non-nuclear losses	$ 750,000,000
Elected deductible waiting period	84 days
Alabama Power
Jointly Owned Utility Plant Interests [Line Items]
Maximum assessment, excluding any applicable state premium taxes	$ 275,000,000
Maximum aggregate amount to be paid in one year	41,000,000
Current maximum annual assessments under NEIL policies	56,000,000
Alabama Power | Positive Outcome of Litigation
Jointly Owned Utility Plant Interests [Line Items]
Outstanding claims		$ 110,000,000
Georgia Power
Jointly Owned Utility Plant Interests [Line Items]
Maximum assessment, excluding any applicable state premium taxes	267,000,000
Maximum aggregate amount to be paid in one year	40,000,000
Current maximum annual assessments under NEIL policies	$ 84,000,000
Georgia Power | Positive Outcome of Litigation
Jointly Owned Utility Plant Interests [Line Items]
Outstanding claims		$ 132,000,000