SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Average AFUDC Composite Rates (Details)	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Alabama Power
Capitalized Contract Cost [Line Items]
Composite rate	7.90%	8.10%	8.10%
Georgia Power
Capitalized Contract Cost [Line Items]
Composite rate	7.70%	7.70%	7.60%
Atlanta Gas Light
Capitalized Contract Cost [Line Items]
Composite rate	7.90%	7.70%	7.40%
Chattanooga Gas
Capitalized Contract Cost [Line Items]
Composite rate	7.10%	7.10%	7.10%
Nicor Gas
Capitalized Contract Cost [Line Items]
Composite rate	4.20%	5.60%	4.60%