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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Amortization of Other Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Finite-Lived Intangible Assets [Line Items]
Amortization associated with other intangible assets	$ 35	$ 38	$ 39
Estimated future amortization
2025	32
2026	27
2027	23
2028	23
2029	23
Southern Power
Finite-Lived Intangible Assets [Line Items]
Amortization associated with other intangible assets	20	20	20
Estimated future amortization
2025	20
2026	20
2027	20
2028	20
2029	19
Southern Company Gas
Estimated future amortization
2025	6
2026	3
2027	0
2028	0
2029	0
Southern Company Gas \| Gas marketing services
Finite-Lived Intangible Assets [Line Items]
Amortization associated with other intangible assets	7	$ 10	$ 11
Operating Revenues
Finite-Lived Intangible Assets [Line Items]
Amortization associated with other intangible assets	$ 20