XML 263 R219.htm IDEA: XBRL DOCUMENT v3.22.0.1
DERIVATIVES - Narrative (Details)
MMBTU in Millions
12 Months Ended
Dec. 31, 2021
USD ($)
MMBTU
Dec. 31, 2020
USD ($)
Derivative [Line Items]    
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints 26  
Estimated pre-tax gains (losses) that will be reclassified from OCI to interest expense for the next 12-month period | $ $ (21,000,000)  
Collateral already posted, aggregate fair value | $   $ 28,000,000
Alabama Power    
Derivative [Line Items]    
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints 6  
Georgia Power    
Derivative [Line Items]    
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints 8  
Mississippi Power    
Derivative [Line Items]    
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints 4  
Southern Power    
Derivative [Line Items]    
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints 8  
Parent Company and Southern Power    
Derivative [Line Items]    
Foreign currency cash flow hedge gain (loss) to be reclassified during next 12 months | $ $ (13,000,000)  
Registrants | Derivative Counterparties    
Derivative [Line Items]    
Collateral already posted, aggregate fair value | $ $ 0