Retirement Benefits - Actuarial Assumptions 2 (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($)
Effect of one percent annual increase or decrease in the assumed medical care cost on APBO and the service and interest cost components
1 Percent increase on benefit obligation	$ 119
1 Percent decrease on benefit obligation	(102)
1 Percent increase on service and interest costs	4
1 Percent decrease on service and interest costs	(4)
Alabama Power [Member]
Effect of one percent annual increase or decrease in the assumed medical care cost on APBO and the service and interest cost components
1 Percent increase on benefit obligation	29
1 Percent decrease on benefit obligation	(25)
1 Percent increase on service and interest costs	1
1 Percent decrease on service and interest costs	(1)
Georgia Power [Member]
Effect of one percent annual increase or decrease in the assumed medical care cost on APBO and the service and interest cost components
1 Percent increase on benefit obligation	58
1 Percent decrease on benefit obligation	(50)
1 Percent increase on service and interest costs	2
1 Percent decrease on service and interest costs	(2)
Gulf Power [Member]
Effect of one percent annual increase or decrease in the assumed medical care cost on APBO and the service and interest cost components
1 Percent increase on benefit obligation	4
1 Percent decrease on benefit obligation	(3)
1 Percent increase on service and interest costs	0
1 Percent decrease on service and interest costs	0
Mississippi Power [Member]
Effect of one percent annual increase or decrease in the assumed medical care cost on APBO and the service and interest cost components
1 Percent increase on benefit obligation	5
1 Percent decrease on benefit obligation	(5)
1 Percent increase on service and interest costs	0
1 Percent decrease on service and interest costs	$ 0