XML 181 R122.htm IDEA: XBRL DOCUMENT v3.10.0.1
Consolidated Entities and Equity Method Investments - SEGCO Equity Method Investments Narrative (Details)
$ in Millions
12 Months Ended
Dec. 31, 2018
USD ($)
MW
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Alabama Power      
Jointly Owned Utility Plant Interests [Line Items]      
Total megawatt capacity | MW 1,000    
Ownership percentage, equity method investment 50.00%    
Percent ownership 14.00%    
Alabama Power | Southern Electric Generating Company      
Jointly Owned Utility Plant Interests [Line Items]      
Total megawatt capacity | MW 1,020    
Share of purchased power $ 102 $ 76 $ 55
Alabama Power | SEGCO      
Jointly Owned Utility Plant Interests [Line Items]      
Dividends paid by equity method investment $ 18 24 24
Georgia Power      
Jointly Owned Utility Plant Interests [Line Items]      
Ownership percentage, equity method investment 50.00%    
Georgia Power | Southern Electric Generating Company      
Jointly Owned Utility Plant Interests [Line Items]      
Share of purchased power $ 105 $ 78  
Purchased Power from Affiliates | Georgia Power | Southern Electric Generating Company      
Jointly Owned Utility Plant Interests [Line Items]      
Share of purchased power     $ 57
SEGCO | Alabama Power      
Jointly Owned Utility Plant Interests [Line Items]      
Percent ownership 86.00%