Introduction - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Related Party Transaction [Line Items]
Net income	$ 936	$ 665
Basic earnings per share (in dollars per share)	$ 0.93	$ 0.66
SOUTHERN Co GAS
Related Party Transaction [Line Items]
Net income	$ 279	$ 239
Goodwill impairment	42	0
ALABAMA POWER CO
Related Party Transaction [Line Items]
Net income	229	178
GEORGIA POWER CO
Related Party Transaction [Line Items]
Net income	352	264
SOUTHERN POWER CO
Related Party Transaction [Line Items]
Net income	115	66
Wholesale Gas Services \| SOUTHERN Co GAS
Related Party Transaction [Line Items]
Inventory write-down	$ 0	$ 0

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of loss from reductions in inventory due to subsequent measurement adjustments, including, but not limited to, physical deterioration, obsolescence, or changes in price levels.

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