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SEGMENT AND RELATED INFORMATION - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($) segment state	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2014
Segment Reporting Information [Line Items]
Total operating revenues	$ 23,463	$ 21,097	$ 22,596
Southern Power
Segment Reporting Information [Line Items]
Total operating revenues	1,605	1,119	1,220
Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues	$ 6,293	5,039	5,598
Number of reportable segments \| segment	3
Number of states in which entity operates \| state	4
Southern Natural Gas Company, LLC \| Southern Company Gas
Segment Reporting Information [Line Items]
Ownership percentage, equity method investment	50.00%
Dalton Pipeline \| Southern Company Gas
Segment Reporting Information [Line Items]
Ownership percentage, equity method investment	50.00%
PennEast Pipeline \| Southern Company Gas
Segment Reporting Information [Line Items]
Ownership percentage, equity method investment	20.00%			20.00%
Atlantic Coast Pipeline \| Southern Company Gas
Segment Reporting Information [Line Items]
Ownership percentage, equity method investment	5.00%
Wholesale revenues, affiliates \| Southern Power \| Traditional Electric Operating Companies
Segment Reporting Information [Line Items]
Total operating revenues	$ 515	364	398
Natural gas \| Southern Company Gas \| Traditional Electric Operating Companies
Segment Reporting Information [Line Items]
Total operating revenues			14
Natural gas \| Southern Company Gas \| Southern Power
Segment Reporting Information [Line Items]
Total operating revenues	$ 18	$ 26	$ 64