Contingencies and Regulatory Matters - Retail Regulatory Matters (Details) - Alabama Power [Member] - USD ($) $ in Millions		Jun. 30, 2015	Dec. 31, 2014
Deferred Under Recovered Regulatory Clause Revenues [Member]
Loss Contingencies [Line Items]
Under Recovered Rate Cnp Balance	[1]	$ 25	$ 2
Rate Cnp Power Purchase Agreement		72	29
Under Recovered Regulatory Clause Revenues [Member]
Loss Contingencies [Line Items]
Under Recovered Rate Cnp Balance, Current		29	47
Rate Cnp Power Purchase Agreement		0	27
Deferred Over Recovered Regulatory Clause Revenues [Member]
Loss Contingencies [Line Items]
Retail Energy Cost Recovery - Over		72	47
Other regulatory liabilities deferred [Member]
Loss Contingencies [Line Items]
Accumulated reserve balance for future storms		$ 81	$ 84

[1] Formerly Known As Rate CNP Environmental