v3.10.0.1
Consolidated Statements of Comprehensive Income (Loss) (Parenthetical) - USD ($)
$ in Millions
6 Months Ended 12 Months Ended
Dec. 31, 2016
Jun. 30, 2016
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Qualifying hedges, change in fair value, tax     $ (16)    
Qualifying hedges, change in fair value, tax       $ 34 $ (84)
Qualifying hedges, reclassification adjustment, tax     24    
Qualifying hedges, reclassification adjustment, tax       (37) 43
Pension and other postretirement benefit plans, gain (loss), tax     (2) 6 10
Pension and other postretirement benefit plans, reclassification adjustment, tax     5 (6) 3
Alabama Power          
Qualifying hedges, change in fair value, tax     0    
Qualifying hedges, change in fair value, tax       (1) (1)
Qualifying hedges, reclassification adjustment, tax     2    
Qualifying hedges, reclassification adjustment, tax       2 2
Georgia Power          
Qualifying hedges, reclassification adjustment, tax     1    
Qualifying hedges, reclassification adjustment, tax       1 2
Mississippi Power          
Qualifying hedges, change in fair value, tax     (1)    
Qualifying hedges, change in fair value, tax       (1) 1
Qualifying hedges, reclassification adjustment, tax     0    
Qualifying hedges, reclassification adjustment, tax       1 1
Southern Power          
Qualifying hedges, change in fair value, tax     (17)    
Qualifying hedges, change in fair value, tax       39 (17)
Qualifying hedges, reclassification adjustment, tax     19    
Qualifying hedges, reclassification adjustment, tax       (46) 36
Pension and other postretirement benefit plans, gain (loss), tax     2 0 0
Pension and other postretirement benefit plans, reclassification adjustment, tax     0 0 $ 0
Southern Company Gas          
Qualifying hedges, change in fair value, tax     2    
Qualifying hedges, change in fair value, tax $ (1)     (3)  
Qualifying hedges, reclassification adjustment, tax     (1)    
Qualifying hedges, reclassification adjustment, tax 0     0  
Pension and other postretirement benefit plans, gain (loss), tax 19   0 0  
Pension and other postretirement benefit plans, reclassification adjustment, tax $ 0   $ 3 $ 0  
Predecessor | Southern Company Gas          
Qualifying hedges, change in fair value, tax   $ (23)      
Qualifying hedges, reclassification adjustment, tax   0      
Pension and other postretirement benefit plans, gain (loss), tax   0      
Pension and other postretirement benefit plans, reclassification adjustment, tax   $ 4