Contingencies and Regulatory Matters - Textual - SO Environmental & FERC Matters (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016
GEORGIA POWER CO
Loss Contingencies [Line Items]
Environmental exit costs, assets previously disposed, liability for remediation		$ 22	$ 17
Claims awarded to companies related to nuclear fuel disposal litigation	$ 18
GULF POWER CO
Loss Contingencies [Line Items]
Environmental exit costs, assets previously disposed, liability for remediation		52	44
SOUTHERN Co GAS
Loss Contingencies [Line Items]
Environmental exit costs, costs accrued to date		388	$ 426
ALABAMA POWER CO
Loss Contingencies [Line Items]
Claims awarded to companies related to nuclear fuel disposal litigation	$ 26
Location One | SOUTHERN Co GAS
Loss Contingencies [Line Items]
Environmental exit costs, assets previously disposed, liability for remediation		$ 2