Electric plant, construction and related agreements - Project Budget and Actual Costs (Details) - Vogtle Units No. 3 & No. 4 $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($)
Project Budget - No Tender
Project-Level Contingency	$ 65
Actual Costs at December 31, 2021
Proceeds from guarantee agreement	1,100
Jointly Owned Nuclear Power Plant
Project Budget - No Tender
Construction Costs	6,459
Financing Costs	1,922
Total Costs	8,381
Project-Level Contingency	98
Oglethorpe-Level Contingency	21
Total Contingency	119
Totals	8,500
Project Budget - Tender
Construction Costs	6,068
Financing Costs	1,914
Total Costs	7,982
Project-Level Contingency	98
Oglethorpe-Level Contingency	20
Total Contingency	118
Totals	8,100
Actual Costs at December 31, 2021
Construction Costs	5,483
Financing Costs	1,502
Total Costs	6,985
Project-Level Contingency	0
Oglethorpe-Level Contingency	0
Total Contingency	0
Totals	$ 6,985