Financing - Short-term Borrowings (Details) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Short-term borrowings
Short-term Debt at the End of the Period, Amount Outstanding	$ 2,032,000,000	$ 1,240,000,000
Short-term Debt at the End of the Period, Weighted Average Interest Rate	1.10%	0.90%
Commercial paper [Member]
Short-term borrowings
Short-term Debt at the End of the Period, Amount Outstanding	$ 1,909,000,000	$ 740,000,000
Short-term Debt at the End of the Period, Weighted Average Interest Rate	1.10%	0.70%
Short-term bank debt [Member]
Short-term borrowings
Short-term Debt at the End of the Period, Amount Outstanding	$ 123,000,000	$ 500,000,000
Short-term Debt at the End of the Period, Weighted Average Interest Rate	1.70%	1.40%
Georgia Power [Member] | Commercial paper [Member]
Short-term borrowings
Short-term Debt at the End of the Period, Amount Outstanding	$ 392,000,000	$ 158,000,000
Short-term Debt at the End of the Period, Weighted Average Interest Rate	1.10%	0.60%
Gulf Power [Member]
Short-term borrowings
Short-term Debt at the End of the Period, Amount Outstanding	$ 268,000,000
Short-term Debt at the End of the Period, Weighted Average Interest Rate	1.20%
Gulf Power [Member] | Commercial paper [Member]
Short-term borrowings
Short-term Debt at the End of the Period, Amount Outstanding	$ 168,000,000	$ 142,000,000
Short-term Debt at the End of the Period, Weighted Average Interest Rate	1.10%	0.70%
Gulf Power [Member] | Short-term bank debt [Member]
Short-term borrowings
Short-term Debt at the End of the Period, Amount Outstanding	$ 100,000,000
Short-term Debt at the End of the Period, Weighted Average Interest Rate	1.50%
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] | Commercial paper [Member]
Short-term borrowings
Short-term Debt at the End of the Period, Amount Outstanding	0	0
Successor [Member] | Commercial paper [Member]
Short-term borrowings
Short-term Debt at the End of the Period, Amount Outstanding	$ 1,257,000,000
Short-term Debt at the End of the Period, Weighted Average Interest Rate	1.03%
Successor [Member] | Southern Company Gas Capital [Member] | Commercial paper [Member]
Short-term borrowings
Short-term Debt at the End of the Period, Amount Outstanding	$ 733,000,000
Short-term Debt at the End of the Period, Weighted Average Interest Rate	1.09%
Successor [Member] | Nicor Gas [Member] | Commercial paper [Member]
Short-term borrowings
Short-term Debt at the End of the Period, Amount Outstanding	$ 524,000,000
Short-term Debt at the End of the Period, Weighted Average Interest Rate	0.95%
Predecessor [Member] | Commercial paper [Member]
Short-term borrowings
Short-term Debt at the End of the Period, Amount Outstanding		$ 1,010,000,000
Short-term Debt at the End of the Period, Weighted Average Interest Rate		0.60%
Predecessor [Member] | Southern Company Gas Capital [Member] | Commercial paper [Member]
Short-term borrowings
Short-term Debt at the End of the Period, Amount Outstanding		$ 471,000,000
Short-term Debt at the End of the Period, Weighted Average Interest Rate		0.71%
Predecessor [Member] | Nicor Gas [Member] | Commercial paper [Member]
Short-term borrowings
Short-term Debt at the End of the Period, Amount Outstanding		$ 539,000,000
Short-term Debt at the End of the Period, Weighted Average Interest Rate		0.52%