Stock Compensation - Schedule of Employees Participating in Stock-Based Compensation Programs (Details)	Dec. 31, 2018 employee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of employees	4,716
Alabama Power
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of employees	745
Georgia Power
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of employees	822
Mississippi Power
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of employees	164
Southern Power
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of employees	95
Southern Company Gas
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of employees	285