Summary of Significant Accounting Policies - Nuclear Decommissiong (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Public Utility, Property, Plant and Equipment [Line Items]
Nuclear decommissioning trusts, at fair value	$ 1,606	$ 1,512
Proceeds from sale of securities held in external trust funds	1,200	1,400	$ 900
Increase (decrease) in fair value of securities related to nuclear decommissioning	114	11	98
Plant Farley [Member]
Decommissioning
Total site study costs	1,442
Plant Farley [Member] | Spent fuel management
Decommissioning
Total site study costs	0
Plant Hatch
Decommissioning
Total site study costs	902
Plant Vogtle Nuclear Units One and Two [Member]
Decommissioning
Total site study costs	804
Equity Securities
Public Utility, Property, Plant and Equipment [Line Items]
Nuclear decommissioning trusts, at fair value	878	817
Debt Securitie
Public Utility, Property, Plant and Equipment [Line Items]
Nuclear decommissioning trusts, at fair value	685	654
Other Securities
Public Utility, Property, Plant and Equipment [Line Items]
Nuclear decommissioning trusts, at fair value	41	38
Unrealized Loss | Securities Held in Funds
Public Utility, Property, Plant and Equipment [Line Items]
Increase (decrease) in fair value of securities related to nuclear decommissioning		(83)
Unrealized Gain | Securities Held in Funds
Public Utility, Property, Plant and Equipment [Line Items]
Increase (decrease) in fair value of securities related to nuclear decommissioning	48		19
Alabama Power [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Decommissioning Fund Investments Net Of Foreign Currency	790	734
Nuclear decommissioning trusts, at fair value	792	737
Proceeds from sale of securities held in external trust funds	351	438	244
Increase (decrease) in fair value of securities related to nuclear decommissioning	76	8	54
Accumulated Provisions for Decommissioning
Accumulated Provisions for Decommissioning	809	754
Decommissioning
Total site study costs	$ 1,442
Significant assumption of inflation rate used to determine the costs for rate making (as percent)	4.50%
Significant assumption of trust earnings rate used to determine the costs for rate making (as percent)	7.00%
Alabama Power [Member] | Accumulated provisions for the external decommissioning trust funds
Accumulated Provisions for Decommissioning
Accumulated Provisions for Decommissioning		734
Alabama Power [Member] | Accumulated Provisions for Decommissioning Internal Reserves [Member]
Accumulated Provisions for Decommissioning
Accumulated Provisions for Decommissioning	$ 19	20
Alabama Power [Member] | Plant Farley [Member] | Plant Farley [Member]
Decommissioning
Beginning Year	2037
Completion Year	2076
Alabama Power [Member] | Plant Farley [Member] | Accumulated provisions for the external decommissioning trust funds
Accumulated Provisions for Decommissioning
Accumulated Provisions for Decommissioning	$ 790	734
Alabama Power [Member] | Plant Farley [Member] | Radiated structures
Decommissioning
Total site study costs	1,362
Alabama Power [Member] | Plant Farley [Member] | Non-radiated structures
Decommissioning
Total site study costs	80
Alabama Power [Member] | Equity Securities
Public Utility, Property, Plant and Equipment [Line Items]
Nuclear decommissioning trusts, at fair value	552	521
Alabama Power [Member] | Debt Securitie
Public Utility, Property, Plant and Equipment [Line Items]
Nuclear decommissioning trusts, at fair value	208	191
Alabama Power [Member] | Other Securities
Public Utility, Property, Plant and Equipment [Line Items]
Nuclear decommissioning trusts, at fair value	30	22
Alabama Power [Member] | Securities Held in Funds
Public Utility, Property, Plant and Equipment [Line Items]
Increase (decrease) in fair value of securities related to nuclear decommissioning		(57)	19
Alabama Power [Member] | Unrealized Gain | Securities Held in Funds
Public Utility, Property, Plant and Equipment [Line Items]
Increase (decrease) in fair value of securities related to nuclear decommissioning	34
Georgia Power [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Fair market value of fund's securities on loan under the Funds' managers' securities lending program	56	76
Fair value of collateral received	58	78
Decommissioning Fund Investments Net Of Foreign Currency	814	775
Nuclear decommissioning trusts, at fair value	814	775
Increase (decrease) in fair value of securities related to nuclear decommissioning	$ 38	3	44
Decommissioning
Significant assumption of inflation rate used to determine the costs for rate making (as percent)	2.40%
Significant assumption of trust earnings rate used to determine the costs for rate making (as percent)	4.40%
Georgia Power [Member] | Plant Hatch
Decommissioning
Beginning Year	2034
Completion Year	2075
Total site study costs	$ 902
Amount expensed for rate making purpose				$ 4
Georgia Power [Member] | Plant Hatch | Accumulated provisions for the external decommissioning trust funds
Accumulated Provisions for Decommissioning
Accumulated Provisions for Decommissioning	511	487
Georgia Power [Member] | Plant Hatch | Radiated structures
Decommissioning
Total site study costs	678
Georgia Power [Member] | Plant Hatch | Spent fuel management
Decommissioning
Total site study costs	160
Georgia Power [Member] | Plant Hatch | Non-radiated structures
Decommissioning
Total site study costs	$ 64
Georgia Power [Member] | Plant Vogtle Nuclear Units One and Two [Member]
Decommissioning
Beginning Year	2047
Completion Year	2079
Total site study costs	$ 804
Georgia Power [Member] | Plant Vogtle Nuclear Units One and Two [Member] | Accumulated provisions for the external decommissioning trust funds
Accumulated Provisions for Decommissioning
Accumulated Provisions for Decommissioning	303	288
Georgia Power [Member] | Plant Vogtle Nuclear Units One and Two [Member] | Radiated structures
Decommissioning
Total site study costs	568
Georgia Power [Member] | Plant Vogtle Nuclear Units One and Two [Member] | Spent fuel management
Decommissioning
Total site study costs	147
Georgia Power [Member] | Plant Vogtle Nuclear Units One and Two [Member] | Non-radiated structures
Decommissioning
Total site study costs	89
Georgia Power [Member] | Plant Vogtle [Member]
Decommissioning
Amount expensed for rate making purpose				$ 2
Georgia Power [Member] | Equity Securities
Public Utility, Property, Plant and Equipment [Line Items]
Nuclear decommissioning trusts, at fair value	326	296
Georgia Power [Member] | Debt Securitie
Public Utility, Property, Plant and Equipment [Line Items]
Nuclear decommissioning trusts, at fair value	477	463
Georgia Power [Member] | Other Securities
Public Utility, Property, Plant and Equipment [Line Items]
Nuclear decommissioning trusts, at fair value	11	16
Georgia Power [Member] | Securities Investment [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Nuclear decommissioning trusts, at fair value	803	980	$ 669
Georgia Power [Member] | Securities Held in Funds
Public Utility, Property, Plant and Equipment [Line Items]
Increase (decrease) in fair value of securities related to nuclear decommissioning	$ 14
Georgia Power [Member] | Unrealized Gain (Loss or Write-down)1 [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Increase (decrease) in fair value of securities related to nuclear decommissioning		$ (26)