Contingencies and Regulatory Matters - Alabama Power Narrative (Details) - ALABAMA POWER CO $ in Millions				3 Months Ended	6 Months Ended	12 Months Ended
	Jan. 01, 2019 $ / KWH_Kilowatt_hour	May 01, 2018 USD ($) $ / KWH_Kilowatt_hour	Apr. 30, 2018 $ / KWH_Kilowatt_hour	Mar. 31, 2018	Dec. 31, 2018 USD ($)	Dec. 31, 2019 USD ($)
Loss Contingencies [Line Items]
Customer refundable fees, refund payments, tranche one, percentage				25.00%
Customer refundable fees, refund payments, tranche two, percentage				40.00%
Customer refundable fees, refund payments, tranche three, percentage				75.00%
Minimum
Loss Contingencies [Line Items]
Public utilities, actual weighted common equity return, threshold, percentage				6.15%
Public utilities, actual weighted common equity return, threshold for customer refundable fees, refund payments, percentage, tranche one				6.15%
Public utilities, actual weighted common equity return, threshold for customer refundable fees, refund payments, percentage, tranche two				6.65%
Public utilities, actual weighted common equity return, threshold for customer refundable fees, refund payments, percentage, tranche three				7.15%
Maximum
Loss Contingencies [Line Items]
Public utilities, actual weighted common equity return, threshold, percentage				7.65%
Public utilities, actual weighted common equity return, threshold for customer refundable fees, refund payments, percentage, tranche one				6.65%
Public utilities, actual weighted common equity return, threshold for customer refundable fees, refund payments, percentage, tranche two				7.15%
Public utilities, actual weighted common equity return, threshold for customer refundable fees, refund payments, percentage, tranche three				7.65%
Customer refundable fees, refund payments, percentage				7.65%
Subsequent Event
Loss Contingencies [Line Items]
Public utilities, approved return on equity percentage		55.00%
Public utilities, allowed weighted common equity return, percentage		6.15%	6.21%
Current billing rates under rate ecr in terms of per units | $ / KWH_Kilowatt_hour		2.353	2.015
Approved increase (decrease) in fuel rates amount		$ 100
Tax Cuts and Jobs Act of 2017, change in tax rate, deferred tax liability, income tax benefit, maximum amount used to offset under recovered amounts		30
Subsequent Event | Minimum
Loss Contingencies [Line Items]
Tax Cuts and Jobs Act of 2017, change in tax rate, deferred tax liability, income tax benefit		30
Subsequent Event | Maximum
Loss Contingencies [Line Items]
Tax Cuts and Jobs Act of 2017, change in tax rate, deferred tax liability, income tax benefit		$ 50
Scenario, Forecast
Loss Contingencies [Line Items]
Customer refundable fees, refund payments					$ 257	$ 50
Current billing rates under rate ecr in terms of per units | $ / KWH_Kilowatt_hour	5.910
Rate RSE | Subsequent Event | Minimum
Loss Contingencies [Line Items]
Public utilities, public service commission, days to accept issuance		3 days
Rate RSE | Subsequent Event | Maximum
Loss Contingencies [Line Items]
Public utilities, public service commission, days to accept issuance		5 days
Rate ECR | Subsequent Event | Minimum
Loss Contingencies [Line Items]
Public utilities, public service commission, days to accept issuance		3 days
Rate ECR | Subsequent Event | Maximum
Loss Contingencies [Line Items]
Public utilities, public service commission, days to accept issuance		5 days