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INTRODUCTION - Narrative (Details) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
INTRODUCTION - Narrative (Details) $ in Millions	Jun. 30, 2020 USD ($) facility	Sep. 30, 2020 USD ($)	Mar. 31, 2020	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Goodwill		$ 5,280		$ 5,280		$ 5,280
SOUTHERN Co GAS
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Goodwill		5,015		5,015		$ 5,015
Inventory decrement					$ 10
ALABAMA POWER CO
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Asset retirement obligation, period increase	$ 462
Number of facilities, closure designs completed \| facility	1
GEORGIA POWER CO
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Asset retirement obligation, period increase		411
PowerSecure
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Goodwill		$ 263		$ 263
Maximum \| Natural Gas Generating Facility \| SOUTHERN POWER CO
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Property, plant and equipment, useful life			45 years	50 years