Contingencies and Regulatory Matters - Retail Regulatory Matters (Details) (Alabama Power [Member], USD $)	Sep. 30, 2014	Dec. 31, 2013
Loss Contingencies [Line Items]
Under recovered rate CNP environmental balance, deferred	$ 0	$ 7,000,000
Under recovered rate CNP environmental balance, current	25,000,000	0
Under recovered rate CNP PPA, deferred	46,000,000	18,000,000
Under recovered rate CNP PPA, current	9,000,000	0
Retail energy cost recovery - over, current	49,000,000	37,000,000
Retail energy cost recovery - over, deferred	0	15,000,000
Natural disaster reserve	87,000,000	96,000,000
Fuel Recovery Clause [Member]
Loss Contingencies [Line Items]
Retail energy cost recovery - over, current	44,000,000	27,000,000
Retail energy cost recovery - over, deferred	$ 0	$ 15,000,000