Acquisitions and Dispositions - Pro Forma Consolidated Information (Details) - Southern Company Gas $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) $ / shares
Business Acquisition [Line Items]
Operating revenues (in millions) | $	$ 21,791
Net income attributable to Southern Company (in millions) | $	$ 2,591
Basic EPS (in dollars per share) | $ / shares	$ 2.70
Diluted EPS (in dollars per share) | $ / shares	$ 2.68