Regulatory Matters - Nuclear Construction Regulatory Matters (Details) - Georgia Power $ in Millions									3 Months Ended	12 Months Ended						48 Months Ended
	Jan. 01, 2021	Jan. 01, 2020	Feb. 19, 2019 USD ($)	Dec. 21, 2018 appeal	Dec. 18, 2018 USD ($)	Aug. 31, 2018 USD ($)	Jan. 01, 2018	Jan. 01, 2016	Jun. 30, 2018 USD ($) subcontractor	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2009 USD ($)	Dec. 31, 2022 USD ($)	Jan. 01, 2013
Loss Contingencies [Line Items]
Proceeds from recovery of financing costs											$ 1,900.0
Retail rate of return on common equity																	10.95%
Potential decrease each month, percentage											0.01%
Number of appeals dismissed | appeal				2
Maximum guarantee											$ 30.0
Approval of construction capital costs						$ 578.0
Plant Vogtle Units 3 And 4
Loss Contingencies [Line Items]
Estimated in-service capital cost															$ 4,418.0
Project capital cost forecast											7,300.0
Increase (decrease) in tariff					$ 88.0
Additional construction capital costs														$ 3,300.0
Amendment to estimated in-service capital cost											5,680.0
Retail rate of return on common equity														10.95%
Public utilities, approved return on equity							10.00%	10.00%
Return on equity reduction, negative impact on earnings											100.0	$ 25.0	$ 20.0
Increase to base capital cost forecast									$ 700.0
Pre-tax charge to income									1,100.0
After-tax charge to income									$ 800.0
Maximum guarantee											$ 1,700.0
Plant Vogtle Units 3 And 4 | Scenario, Forecast
Loss Contingencies [Line Items]
Public utilities, approved return on equity	5.30%	8.30%
Return on equity reduction, negative impact on earnings										$ 75.0						$ 615.0
Subsequent Event
Loss Contingencies [Line Items]
Approval of construction capital costs			$ 5,400.0
Expenditures related to Georgia Power's portion of an administrative claim filed in the Westinghouse bankruptcy proceedings			$ 51.6
Minimum
Loss Contingencies [Line Items]
Retail rate of return on common equity																	10.00%
Minimum | Plant Vogtle Units 3 And 4
Loss Contingencies [Line Items]
Number of subcontractors (more than) | subcontractor									60