Contingencies and Regulatory Matters - Recovery Balance of Each Regulatory Clause - Alabama Power (Details) - Alabama Power [Member] - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Under recovered regulatory clause revenues, current [Member]
Loss Contingencies [Line Items]
Rate CNP Compliance	$ 22	$ 43
Deferred under recovered regulatory clause revenues [Member]
Loss Contingencies [Line Items]
Rate CNP PPA	105	99
Other regulatory liabilities, current [Member]
Loss Contingencies [Line Items]
Retail Energy Cost Recovery	173	238
Deferred Over Recovered Regulatory Clause Revenues [Member]
Loss Contingencies [Line Items]
Retail Energy Cost Recovery	64	0
Other regulatory liabilities, deferred [Member]
Loss Contingencies [Line Items]
Natural Disaster Reserve	$ 74	$ 75