Vogtle Units No. 3 and No. 4 Construction Project (Details) - Vogtle Units Number 3 And Number 4		1 Months Ended		3 Months Ended	12 Months Ended
	Jan. 11, 2018 item	Nov. 30, 2017 USD ($)	Jul. 31, 2017	Mar. 31, 2018 USD ($) item	Dec. 31, 2008 item MW
Electric plant, construction and related agreements
Total investment in additional vogtle units | $				$ 3,160,067,000
Number of petitions filed by parties | item	2
Ownership participation agreement
Electric plant, construction and related agreements
Number of additional nuclear units | item				2
Ownership interest (as a percent)				30.00%
Ownership participation agreement | Minimum | Occurrence of certain adverse events
Electric plant, construction and related agreements
Ownership interests voting required to continue construction (as a percent)		90.00%
Increase in project budget | $		$ 1,000,000,000
Project extension term		1 year
Ownership approval to change primary construction contractor (as a percent)		90.00%
Ownership approval required for material amendments (as a percent)		67.00%
Engineering, Procurement and Construction Agreement (the EPC Agreement) | Westinghouse Electric Company LLC and Stone & Webster, Inc.
Electric plant, construction and related agreements
Number of nuclear units | item					2
Generating capacity of each nuclear unit | MW					1,100
Project budget | $				$ 7,000,000,000
Amended and Restated Services Agreement | Westinghouse Electric Company LLC and Stone & Webster, Inc.
Electric plant, construction and related agreements
Written notice period for termination of agreement			30 days