Summary of Significant Accounting Policies - Accumulated Provisions and Estimated Costs For Decommissioning (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2012
Alabama Power [Member]
Accumulated Provisions for Decommissioning
Total	$ 626	$ 626
Decommissioning
Total site study costs		1,132
Alabama Power [Member] | Plant Farley [Member]
Decommissioning
Beginning Year	2037	2037
Completion Year	2065	2065
Alabama Power [Member] | Accumulated Provisions for Decommissioning External Trust Funds [Member]
Accumulated Provisions for Decommissioning
Total	604	604
Alabama Power [Member] | Accumulated Provisions for Decommissioning Internal Reserves [Member]
Accumulated Provisions for Decommissioning
Total	22	22
Alabama Power [Member] | Site Study Cost Radiated Structures [Member]
Decommissioning
Total site study costs		1,060
Alabama Power [Member] | Site Study Cost Non-Radiated Structures [Member]
Decommissioning
Total site study costs		72
Plant Farley [Member]
Accumulated Provisions for Decommissioning
Total	626	626
Decommissioning
Beginning Year	2037	2037
Completion Year	2065	2065
Total site study costs		1,132
Plant Farley [Member] | Accumulated Provisions for Decommissioning External Trust Funds [Member]
Accumulated Provisions for Decommissioning
Total	604	604
Plant Farley [Member] | Accumulated Provisions for Decommissioning Internal Reserves [Member]
Accumulated Provisions for Decommissioning
Total	22	22
Plant Farley [Member] | Site Study Cost Radiated Structures [Member]
Decommissioning
Total site study costs		1,060
Plant Farley [Member] | Site Study Cost Non-Radiated Structures [Member]
Decommissioning
Total site study costs		72
Plant Hatch [Member]
Accumulated Provisions for Decommissioning
Total	435	435
Decommissioning
Beginning Year	2034	2034
Completion Year	2068	2068
Total site study costs		731
Plant Hatch [Member] | Accumulated Provisions for Decommissioning External Trust Funds [Member]
Accumulated Provisions for Decommissioning
Total	435	435
Plant Hatch [Member] | Accumulated Provisions for Decommissioning Internal Reserves [Member]
Accumulated Provisions for Decommissioning
Total	0	0
Plant Hatch [Member] | Site Study Cost Radiated Structures [Member]
Decommissioning
Total site study costs		680
Plant Hatch [Member] | Site Study Cost Non-Radiated Structures [Member]
Decommissioning
Total site study costs		51
Plant Hatch [Member] | Georgia Power [Member]
Decommissioning
Beginning Year	2034	2034
Completion Year	2068	2068
Total site study costs		731
Net Assets Of The Funds	435
Plant Hatch [Member] | Georgia Power [Member] | Site Study Cost Radiated Structures [Member]
Decommissioning
Total site study costs		549
Plant Hatch [Member] | Georgia Power [Member] | Spent Fuel Management [Member]
Decommissioning
Total site study costs		131
Plant Hatch [Member] | Georgia Power [Member] | Site Study Cost Non-Radiated Structures [Member]
Decommissioning
Total site study costs		51
Plant Vogtle [Member]
Accumulated Provisions for Decommissioning
Total	256	256
Decommissioning
Beginning Year	2047	2047
Completion Year	2072	2072
Total site study costs		644
Plant Vogtle [Member] | Accumulated Provisions for Decommissioning External Trust Funds [Member]
Accumulated Provisions for Decommissioning
Total	256	256
Plant Vogtle [Member] | Accumulated Provisions for Decommissioning Internal Reserves [Member]
Accumulated Provisions for Decommissioning
Total	0	0
Plant Vogtle [Member] | Site Study Cost Radiated Structures [Member]
Decommissioning
Total site study costs		568
Plant Vogtle [Member] | Site Study Cost Non-Radiated Structures [Member]
Decommissioning
Total site study costs		76
Plant Vogtle [Member] | Georgia Power [Member]
Decommissioning
Beginning Year	2047	2047
Completion Year	2072	2072
Total site study costs		644
Net Assets Of The Funds	256
Plant Vogtle [Member] | Georgia Power [Member] | Site Study Cost Radiated Structures [Member]
Decommissioning
Total site study costs		453
Plant Vogtle [Member] | Georgia Power [Member] | Spent Fuel Management [Member]
Decommissioning
Total site study costs		115
Plant Vogtle [Member] | Georgia Power [Member] | Site Study Cost Non-Radiated Structures [Member]
Decommissioning
Total site study costs		$ 76