Income Taxes - Summary of Operating Loss Carryforwards Valuation Allowances (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Operating Loss Carryforwards [Line Items]
Valuation allowance	$ 142	$ 112
GEORGIA POWER CO
Operating Loss Carryforwards [Line Items]
Valuation allowance	58	28
Federal
Operating Loss Carryforwards [Line Items]
Valuation allowance	20	20
Federal | GEORGIA POWER CO
Operating Loss Carryforwards [Line Items]
Valuation allowance	0	0
State (net of federal benefit)
Operating Loss Carryforwards [Line Items]
Valuation allowance	122	92
State (net of federal benefit) | GEORGIA POWER CO
Operating Loss Carryforwards [Line Items]
Valuation allowance	$ 58	$ 28