RETIREMENT BENEFITS - 401K Plan Matching Contributions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost	$ 148	$ 137	$ 131
Alabama Power
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost	30	29	28
Georgia Power
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost	36	31	31
Mississippi Power
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost	5	5	5
Southern Power
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost	3	3	3
Southern Company Gas
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost	$ 21	$ 20	$ 18