Contingencies and Regulatory Matters - Retail Regulatory Matters (Details) (Alabama Power [Member], USD $) In Millions, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Deferred Under Recovered Regulatory Clause Revenues [Member]
Loss Contingencies [Line Items]
Under Recovered Rate Cnp Balance	$ 25	[1]	$ 2	[1]
Rate Cnp Power Purchase Agreement	62		29
Under Recovered Regulatory Clause Revenues [Member]
Loss Contingencies [Line Items]
Under Recovered Rate Cnp Balance, Current	16		47
Rate Cnp Power Purchase Agreement	0		27
Deferred Over Recovered Regulatory Clause Revenues [Member]
Loss Contingencies [Line Items]
Retail Energy Cost Recovery - Over	81		47
Other regulatory liabilities deferred [Member]
Loss Contingencies [Line Items]
Accumulated reserve balance for future storms	$ 82		$ 84

[1] Formerly Known As Rate CNP Environmental