v3.7.0.1
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