Financing - Short-term Borrowings (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Short-term Debt [Line Items]
Expires, 2017	$ 1,665
Short-term borrowings
Short-term Debt at the End of the Period, Amount Outstanding	$ 1,240	$ 803
Short-term Debt at the End of the Period, Weighted Average Interest Rate	0.90%	0.30%
Commercial paper [Member]
Short-term borrowings
Short-term Debt at the End of the Period, Amount Outstanding	$ 740	$ 803
Short-term Debt at the End of the Period, Weighted Average Interest Rate	0.70%	0.30%
Short-term bank debt [Member]
Short-term borrowings
Short-term Debt at the End of the Period, Amount Outstanding	$ 500	$ 0
Short-term Debt at the End of the Period, Weighted Average Interest Rate	1.40%	0.00%
Parent Company [Member]
Short-term Debt [Line Items]
Expires, 2017	$ 1,000
Georgia Power [Member]
Short-term Debt [Line Items]
Expires, 2017	0
Georgia Power [Member] | Commercial paper [Member]
Short-term borrowings
Short-term Debt at the End of the Period, Amount Outstanding	$ 158	$ 156
Short-term Debt at the End of the Period, Weighted Average Interest Rate	0.60%	0.30%
Alabama Power [Member]
Short-term Debt [Line Items]
Expires, 2017	$ 500
Gulf Power [Member]
Short-term Debt [Line Items]
Expires, 2017	165
Gulf Power [Member] | Commercial paper [Member]
Short-term borrowings
Short-term Debt at the End of the Period, Amount Outstanding	$ 142	$ 110
Short-term Debt at the End of the Period, Weighted Average Interest Rate	0.70%	0.30%
Mississippi Power [Member]
Short-term Debt [Line Items]
Expires, 2017	$ 0
Mississippi Power [Member] | Commercial paper [Member]
Short-term borrowings
Short-term Debt at the End of the Period, Amount Outstanding	0	$ 0
Southern Power [Member]
Short-term Debt [Line Items]
Expires, 2017	0
Southern Power [Member] | Commercial paper [Member]
Short-term borrowings
Short-term Debt at the End of the Period, Amount Outstanding	0	$ 195
Short-term Debt at the End of the Period, Weighted Average Interest Rate		0.40%
Other Subsidiaries [Member]
Short-term Debt [Line Items]
Expires, 2017	$ 0