SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Total AFUDC and Interest Capitalized (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Capitalized Contract Cost [Line Items]
Total AFUDC and interest capitalized	$ 339	$ 400	$ 327
Alabama Power
Capitalized Contract Cost [Line Items]
Total AFUDC and interest capitalized	76	109	90
Georgia Power
Capitalized Contract Cost [Line Items]
Total AFUDC and interest capitalized	209	251	213
Southern Power
Capitalized Contract Cost [Line Items]
Total AFUDC and interest capitalized	7	3	0
Southern Company Gas
Capitalized Contract Cost [Line Items]
Total AFUDC and interest capitalized	$ 47	$ 37	$ 24