Regulatory Matters - Alabama Power (Details) - USD ($) $ in Millions	Apr. 15, 2019	Mar. 31, 2019	Feb. 28, 2019	Dec. 31, 2018
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Plant in service, net of depreciation		$ (71,839)		$ (72,668)
Other utility plant, net		1,315		0
ALABAMA POWER CO
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Plant in service, net of depreciation		(19,363)		(20,414)
Other utility plant, net		$ 1,315		$ 0
ALABAMA POWER CO | Restatement Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Plant in service, net of depreciation			$ 1,300
Other utility plant, net			$ 1,300
ALABAMA POWER CO | Subsequent Event | Restatement Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Capitalized asset retirement costs, net	$ 700
Regulatory asset to be recovered over the units' remaining useful lives	700
ALABAMA POWER CO | Plant Gorgas Units 8, 9, and 10 | Subsequent Event | Restatement Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net investment costs	740
Regulatory asset to be recovered over the units' remaining useful lives	$ 740