Regulatory Matters - Nuclear Construction (Details) - GEORGIA POWER CO $ in Millions								1 Months Ended		9 Months Ended	12 Months Ended				36 Months Ended
	Jan. 01, 2021	Jan. 01, 2020	Nov. 01, 2019 USD ($)	Aug. 30, 2019 USD ($)	Feb. 19, 2019 USD ($)	Jan. 11, 2018 USD ($)	Jan. 01, 2016	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) appeal	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2012 utility MW	Dec. 31, 2009 USD ($)	Dec. 31, 2022 USD ($)	Aug. 31, 2018	Dec. 31, 2014	Dec. 31, 2013
Loss Contingencies [Line Items]
Number of construction units approved | utility													2
Electric generating capacity in mega watts under consortium agreement | MW													1,100
Estimated in-service capital cost														$ 4,418.0
Financing costs collected, net of tax										$ 2,100.0
Increase (decrease) in NCCR 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%
Number of appeals | appeal									2
Requested capital construction costs				$ 1,200.0	$ 5,400.0
Deferred approval of expenditures related to administrative claim				21.5	$ 51.6
Refund of construction capital costs				$ 30.1
Scenario, Forecast
Loss Contingencies [Line Items]
Increase (decrease) in NCCR tariff			$ (65.0)
FFB Loan
Loss Contingencies [Line Items]
Long-term line of credit										$ 3,460.0
Eligible project costs to be reimbursed								$ 5,130.0
Plant Vogtle Units 3 And 4
Loss Contingencies [Line Items]
Proportionate ownership share										45.70%
Construction contingency estimate, subject to rate recovery evaluation										$ 30.0
Construction financing costs										2,100.0
Base project capital cost forecast, monthly										50.0
Monthly AFUDC										11.0
Percentage of ownership interest required for voting for continuing construction																90.00%	90.00%
Cost settlement agreement revised forecast, net of payments										$ 7,300.0
Public utilities, approved return on equity percentage							10.00%
Public utilities, approved return on equity, monthly percentage decrease										0.10%
Return on equity reduction, negative impact on earnings												$ 100.0
Guarantor obligations										$ 1,700.0
Customer refund										$ 188.0
Plant Vogtle Units 3 And 4 | Scenario, Forecast
Loss Contingencies [Line Items]
Construction financing costs											$ 3,100.0
Public utilities, approved return on equity percentage	5.30%	8.30%
Return on equity reduction, negative impact on earnings											$ 70.0				$ 650.0
Plant Vogtle Units 3 And 4 | Vogtle Owners
Loss Contingencies [Line Items]
Period of notice required in the event letters of credit are not renewed										30 days