Contingencies and Regulatory Matters - Recovery Balance of Each Regulatory Clause - Alabama Power (Details) - Alabama Power [Member] - USD ($) $ in Millions	Mar. 31, 2017	Feb. 17, 2017	Dec. 31, 2016
Deferred under recovered regulatory clause revenues [Member]
Loss Contingencies [Line Items]
Rate CNP Compliance	$ 0		$ 9
Rate CNP PPA	0		142
Under recovered regulatory clause revenues [Member]
Loss Contingencies [Line Items]
Rate CNP PPA	3		0
Other regulatory liabilities, current [Member]
Loss Contingencies [Line Items]
Retail Energy Cost Recovery	40		76
Other regulatory liabilities, deferred [Member]
Loss Contingencies [Line Items]
Natural Disaster Reserve	$ 66		$ 69
Regulatory Assets, Deferred [Member]
Loss Contingencies [Line Items]
Over (under) recovered environmental clause		$ 23