Vogtle Units No. 3 and No. 4 Construction Project (Details) - Vogtle Units No. 3 & No. 4	9 Months Ended	12 Months Ended
	Sep. 30, 2019 USD ($) item	Dec. 31, 2008 item MW	Apr. 30, 2019 USD ($)
Public Utility Property Plant and Equipment
Project budget			$ 7,500,000,000
Current project level budget	$ 800,000,000
Percentage of interest in current project level budget	30.00%
Interest in current project level budget (Value)	$ 240,000,000
Allocated project level contingency	67,000,000
Allocated project level contingency from interest in project level budget	20,000,000
Total investment in additional Vogtle units	$ 4,621,837,000
Ownership participation agreement
Public Utility Property Plant and Equipment
Number of additional nuclear units | item	2
Ownership interest (as a percent)	30.00%
Ownership participation agreement | Occurrence of certain adverse events
Public Utility Property Plant and Equipment
Percentage of costs disallowed for recovery	6.00%
Project extension term	1 year
Ownership participation agreement | Minimum | Occurrence of certain adverse events
Public Utility Property Plant and Equipment
Ownership interests voting required to continue construction (as a percent)	90.00%
EPC Agreement | Westinghouse Electric Company LLC and Stone & Webster, Inc.
Public Utility Property Plant and Equipment
Number of nuclear units | item		2
Generating capacity of each nuclear unit | MW		1,100
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