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Vogtle Units No. 3 and No. 4 Construction Project - Narrative (Details)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2021
USD ($)
Mar. 31, 2021
USD ($)
Dec. 31, 2020
USD ($)
Mar. 31, 2009
unit
MW
Jun. 30, 2021
USD ($)
unit
Vogtle Units No. 3 & No. 4          
Public Utility Property Plant and Equipment          
Ownership interest (as a percent) 30.00%       30.00%
Total investment in additional Vogtle units $ 6,500.0       $ 6,500.0
Additional construction contingency, total 260.0 $ 106.0 $ 375.0    
Project-Level Contingency 78.0 32.0 $ 112.5    
Additional construction contingency, construction productivity and field support 746.0 183.0      
Ownership amount of additional construction contingency, construction productivity and field support 224.0 55.0      
Project level contingency 300.0        
Ownership amount of project level contingency $ 90.0        
Construction financing         $ 80.0
Delay period         3 months
Monthly delay cost         $ 55.0
Vogtle Units No. 3 & No. 4 | Minimum          
Public Utility Property Plant and Equipment          
COVID related costs         352.0
Ownership amount of COVID related costs         106.0
Vogtle Units No. 3 & No. 4 | Maximum          
Public Utility Property Plant and Equipment          
COVID related costs         442.0
Ownership amount of COVID related costs         $ 133.0
Vogtle Units No. 3 & No. 4 | Ownership participation agreement          
Public Utility Property Plant and Equipment          
Number of additional nuclear units | unit         2
Ownership interest (as a percent) 30.00%       30.00%
Project budget   $ 7,500.0     $ 8,250.0
Project extension term         1 year
Vogtle Units No. 3 & No. 4 | EPC Agreement | Westinghouse Electric Company LLC and Stone & Webster, Inc.          
Public Utility Property Plant and Equipment          
Number of nuclear units | unit       2  
Generating capacity of each nuclear unit | MW       1,100  
Vogtle Units No. 3 & No. 4 | Services Agreement | Westinghouse Electric Company LLC and Stone & Webster, Inc.          
Public Utility Property Plant and Equipment          
Written notice period for termination of agreement         30 days
Vogtle Units No. 3 & No. 4 | Global Amendments To Term Sheet          
Public Utility Property Plant and Equipment          
Percentage of costs disallowed for recovery 6.00%       6.00%
Vogtle Units No. 3 & No. 4 | Global Amendments To Term Sheet | Minimum          
Public Utility Property Plant and Equipment          
Percentage of ownership approval to change primary construction contractor 90.00%       90.00%
Vogtle Unit Number 4          
Public Utility Property Plant and Equipment          
Monthly delay cost         $ 25.0