Summary of Significant Accounting Policies - Accumulated Provisions and Estimated Costs For Decommissioning (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Alabama Power [Member]
Accumulated Provisions for Decommissioning
Accumulated Provisions for Decommissioning	$ 754	$ 775
Decommissioning
Total site study costs	$ 1,442
Alabama Power [Member] | Plant Farley [Member]
Decommissioning
Beginning Year	2037
Completion Year	2076
Alabama Power [Member] | Accumulated Provisions for Decommissioning External Trust Funds [Member]
Accumulated Provisions for Decommissioning
Accumulated Provisions for Decommissioning	$ 734	754
Alabama Power [Member] | Accumulated Provisions for Decommissioning Internal Reserves [Member]
Accumulated Provisions for Decommissioning
Accumulated Provisions for Decommissioning	20	21
Alabama Power [Member] | Site Study Cost Radiated Structures [Member]
Decommissioning
Total site study costs	1,362
Alabama Power [Member] | Site Study Cost Non-Radiated Structures [Member]
Decommissioning
Total site study costs	$ 80
Plant Farley [Member]
Decommissioning
Beginning Year	2037
Completion Year	2076
Total site study costs	$ 1,442
Plant Farley [Member] | Site Study Cost Radiated Structures [Member]
Decommissioning
Total site study costs	1,362
Plant Farley [Member] | Spent Fuel Management [Member]
Decommissioning
Total site study costs	0
Plant Farley [Member] | Site Study Cost Non-Radiated Structures [Member]
Decommissioning
Total site study costs	80
Plant Farley [Member] | Alabama Power [Member]
Accumulated Provisions for Decommissioning
Accumulated Provisions for Decommissioning	754	775
Plant Farley [Member] | Alabama Power [Member] | Accumulated Provisions for Decommissioning External Trust Funds [Member]
Accumulated Provisions for Decommissioning
Accumulated Provisions for Decommissioning	734	754
Plant Farley [Member] | Alabama Power [Member] | Accumulated Provisions for Decommissioning Internal Reserves [Member]
Accumulated Provisions for Decommissioning
Accumulated Provisions for Decommissioning	$ 20	21
Plant Hatch [Member]
Decommissioning
Beginning Year	2034
Completion Year	2075
Total site study costs	$ 902
Plant Hatch [Member] | Site Study Cost Radiated Structures [Member]
Decommissioning
Total site study costs	678
Plant Hatch [Member] | Spent Fuel Management [Member]
Decommissioning
Total site study costs	160
Plant Hatch [Member] | Site Study Cost Non-Radiated Structures [Member]
Decommissioning
Total site study costs	64
Plant Hatch [Member] | Georgia Power [Member]
Accumulated Provisions for Decommissioning
Accumulated Provisions for Decommissioning	$ 487	496
Decommissioning
Beginning Year	2034
Completion Year	2075
Total site study costs	$ 902
Plant Hatch [Member] | Georgia Power [Member] | Accumulated Provisions for Decommissioning External Trust Funds [Member]
Accumulated Provisions for Decommissioning
Accumulated Provisions for Decommissioning	487	496
Plant Hatch [Member] | Georgia Power [Member] | Accumulated Provisions for Decommissioning Internal Reserves [Member]
Accumulated Provisions for Decommissioning
Accumulated Provisions for Decommissioning	0	0
Plant Hatch [Member] | Georgia Power [Member] | Site Study Cost Radiated Structures [Member]
Decommissioning
Total site study costs	678
Plant Hatch [Member] | Georgia Power [Member] | Spent Fuel Management [Member]
Decommissioning
Total site study costs	160
Plant Hatch [Member] | Georgia Power [Member] | Site Study Cost Non-Radiated Structures [Member]
Decommissioning
Total site study costs	$ 64
Plant Vogtle Units 1 and 2 [Member]
Decommissioning
Beginning Year	2047
Completion Year	2079
Total site study costs	$ 804
Plant Vogtle Units 1 and 2 [Member] | Site Study Cost Radiated Structures [Member]
Decommissioning
Total site study costs	568
Plant Vogtle Units 1 and 2 [Member] | Spent Fuel Management [Member]
Decommissioning
Total site study costs	147
Plant Vogtle Units 1 and 2 [Member] | Site Study Cost Non-Radiated Structures [Member]
Decommissioning
Total site study costs	89
Plant Vogtle Units 1 and 2 [Member] | Georgia Power [Member]
Accumulated Provisions for Decommissioning
Accumulated Provisions for Decommissioning	$ 288	293
Decommissioning
Beginning Year	2047
Completion Year	2079
Total site study costs	$ 804
Plant Vogtle Units 1 and 2 [Member] | Georgia Power [Member] | Accumulated Provisions for Decommissioning External Trust Funds [Member]
Accumulated Provisions for Decommissioning
Accumulated Provisions for Decommissioning	288	293
Plant Vogtle Units 1 and 2 [Member] | Georgia Power [Member] | Accumulated Provisions for Decommissioning Internal Reserves [Member]
Accumulated Provisions for Decommissioning
Accumulated Provisions for Decommissioning	0	$ 0
Plant Vogtle Units 1 and 2 [Member] | Georgia Power [Member] | Site Study Cost Radiated Structures [Member]
Decommissioning
Total site study costs	568
Plant Vogtle Units 1 and 2 [Member] | Georgia Power [Member] | Spent Fuel Management [Member]
Decommissioning
Total site study costs	147
Plant Vogtle Units 1 and 2 [Member] | Georgia Power [Member] | Site Study Cost Non-Radiated Structures [Member]
Decommissioning
Total site study costs	$ 89