Regulatory Matters - GPC Nuclear Construction (Details) $ in Millions	3 Months Ended				9 Months Ended		12 Months Ended
	Sep. 30, 2021 USD ($)	Jun. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2012 utility MW	Aug. 31, 2018
Loss Contingencies [Line Items]
Estimated loss on Plant Vogtle Units 3 and 4	$ 264			$ 0	$ 772	$ 149
GEORGIA POWER CO
Loss Contingencies [Line Items]
Estimated loss on Plant Vogtle Units 3 and 4	264	$ 460	$ 48	$ 0	772	149
Estimated loss on Plant Vogtle Units 3 and 4, net of tax	$ 197	343	36		$ 576	$ 111
GEORGIA POWER CO | Plant Vogtle Units 3 And 4
Loss Contingencies [Line Items]
Proportionate ownership share	45.70%				45.70%
Number of construction units approved | utility							2
Electric generating capacity in mega watts under consortium agreement | MW							1,100
Estimated cost to complete, construction contingency estimate, financing costs	$ 3,200				$ 3,200
Estimated cost to complete, construction contingency estimate, financing costs, incurred to date	2,800				2,800
Construction contingency estimate	127	341	84		127
Construction contingency estimate, additional amount	137	$ 119	$ 48		137
Base project capital cost forecast, monthly					25
Monthly AFUDC					$ 15
Percentage of ownership interest required for voting for continuing construction								90.00%
GEORGIA POWER CO | 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
Minimum | GEORGIA POWER CO | Plant Vogtle Units 3 And 4 | COVID-19
Loss Contingencies [Line Items]
Loss contingency, estimate of possible loss, loss of productivity, term					3 months
Estimate of possible loss	160				$ 160
Maximum | GEORGIA POWER CO | Plant Vogtle Units 3 And 4 | COVID-19
Loss Contingencies [Line Items]
Loss contingency, estimate of possible loss, loss of productivity, term					4 months
Estimate of possible loss	$ 200				$ 200