Vogtle Units No. 3 and No. 4 Construction Project - Project Budget and Actual Costs (Details) - Vogtle Units No. 3 & No. 4 - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Project Budget
Project-Level Contingency	$ 32.0	$ 112.5
Remaining Project Budget
Proceeds from guarantee agreement	1,100.0
Jointly Owned Nuclear Power Plant
Project Budget
Construction Costs	5,614.0
Financing Costs	1,592.0
Total Costs	7,206.0
Project-Level Contingency	90.0
Oglethorpe-Level Contingency	204.0
Total Contingency	294.0
Total Contingency	7,500.0
Actual Costs
Construction Costs	4,947.0
Financing Costs	1,328.0
Total Costs	6,275.0
Project-Level Contingency	0.0
Oglethorpe-Level Contingency	0.0
Total Contingency	0.0
Totals	6,275.0
Remaining Project Budget
Construction Costs	667.0
Financing Costs	264.0
Total Costs	931.0
Project-Level Contingency	90.0
Oglethorpe-Level Contingency	204.0
Total Contingency	294.0
Totals	$ 1,225.0