Regulatory Matters - Cost Recovery Clauses (Details) - USD ($) $ in Millions	Sep. 30, 2019	Feb. 05, 2019	Dec. 31, 2018
ALABAMA POWER CO
Loss Contingencies [Line Items]
Rate RSE Refund Liability		$ 75
ALABAMA POWER CO | Deferred under recovered regulatory clause revenues
Loss Contingencies [Line Items]
Rate CNP Compliance	$ 0		$ 42
Rate CNP PPA	45		25
Retail Energy Cost Recovery	0		109
ALABAMA POWER CO | Other regulatory liabilities, deferred
Loss Contingencies [Line Items]
Rate CNP Compliance	55		0
Retail Energy Cost Recovery	21		0
Natural Disaster Reserve	23		20
GEORGIA POWER CO | Receivables – under recovered fuel clause revenues
Loss Contingencies [Line Items]
Fuel Cost Recovery	0		115
GEORGIA POWER CO | Other deferred credits and liabilities
Loss Contingencies [Line Items]
Fuel Cost Recovery	(1)		0
MISSISSIPPI POWER CO | Over recovered regulatory clause liabilities
Loss Contingencies [Line Items]
Fuel Cost Recovery	$ (18)		$ (8)