Electric plant, construction and related agreements - Project Budget and Actual Costs (Details) - Vogtle Units No. 3 & No. 4 - USD ($) $ in Millions		12 Months Ended
	Feb. 18, 2019	Dec. 31, 2022
Actual Costs at December 31, 2022
Proceeds from guarantee agreement		$ 1,100
Cost sharing benefits		99
Global Amendments to Term Sheet
Project Budget (Tender)
Totals		17,100
Actual Costs at December 31, 2022
Additional construction costs	$ 800
Financial Exposure Term Two | Maximum | Global Amendments to Term Sheet
Actual Costs at December 31, 2022
Additional construction costs	$ 2,100
Jointly Owned Nuclear Power Plant
Project Budget (Tender)
Construction Costs		6,554
Freeze Capital Credit		(528)
Financing Costs		2,025
Subtotal		8,051
Deferred Training Costs		47
Total Project Costs Before Contingency		8,098
Oglethorpe Contingency		2
Totals		8,100
Actual Costs at December 31, 2022
Construction Costs		6,147
Freeze Capital Credit		0
Financing Costs		1,770
Subtotal		7,917
Deferred Training Costs		46
Total Project Costs Before Contingency		7,963
Oglethorpe Contingency		0
Totals		7,963
Jointly Owned Nuclear Power Plant | Global Amendments to Term Sheet
Project Budget (Tender)
Totals		$ 17,100