Regulatory Matters - Cost Recovery Clauses (Details) - USD ($) $ in Millions	Mar. 31, 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	21		25
Retail Energy Cost Recovery()	0		109
ALABAMA POWER CO | Customer accounts receivable
Loss Contingencies [Line Items]
Rate CNP Compliance	25		0
ALABAMA POWER CO | Other regulatory liabilities, deferred
Loss Contingencies [Line Items]
Retail Energy Cost Recovery()	2		0
Natural Disaster Reserve	22		20
GEORGIA POWER CO | Receivables – under recovered fuel clause revenues
Loss Contingencies [Line Items]
Fuel Cost Recovery	73		115
MISSISSIPPI POWER CO | Over recovered retail fuel costs
Loss Contingencies [Line Items]
Fuel Cost Recovery	$ 10		$ 8