Acquisitions - Schedule of Acquisitions (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Goodwill	$ 6,251	$ 6,251
Southern Company Gas [Member]
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Current assets	1,557
Intangible assets	400
Property, plant, and equipment	10,108
Goodwill	5,967
Regulatory assets	1,118
Other assets	229
Current liabilities	(2,201)
Deferred credits and other liabilities	(4,742)
Long-term debt	(4,261)
Noncontrolling interest	(174)
Total purchase price	8,001
PowerSecure International, Inc. [Member]
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Current assets	172
Intangible assets	101
Property, plant, and equipment	46
Goodwill	282
Other assets	4
Current liabilities	(114)
Long-term debt, including current portion	48
Deferred credits and other liabilities	(14)
Total purchase price	429
Southern Power [Member]
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Goodwill	$ 2	$ 2