Contingencies and Regulatory Matters - Recovery Balance of Each Regulatory Clause - Alabama Power (Details) - Alabama Power [Member] - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Under recovered regulatory clause revenues, current [Member]
Loss Contingencies [Line Items]
Rate CNP Compliance	$ 7	$ 43
Deferred under recovered regulatory clause revenues [Member]
Loss Contingencies [Line Items]
Rate CNP Compliance	21	0
Rate CNP PPA	115	99
Other regulatory liabilities, current [Member]
Loss Contingencies [Line Items]
Retail Energy Cost Recovery	75	238
Deferred Over Recovered Regulatory Clause Revenues [Member]
Loss Contingencies [Line Items]
Retail Energy Cost Recovery	102	0
Other regulatory liabilities, deferred [Member]
Loss Contingencies [Line Items]
Natural Disaster Reserve	$ 72	$ 75