Summary of Significant Accounting Policies - Environmental Recovery (Details) - GEORGIA POWER CO - USD ($) $ in Millions	1 Months Ended
	Dec. 31, 2013	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Line Items]
Environmental exit costs, assets previously disposed, liability for remediation		$ 22	$ 17
Environmental regulatory assets		49	35
Environmental Remediation Reserve
Accounting Policies [Line Items]
Costs recovered annually under rate plan	$ 2
Other regulatory assets current
Accounting Policies [Line Items]
Environmental regulatory assets		2	2
Other regulatory assets deferred
Accounting Policies [Line Items]
Environmental regulatory assets		$ 47	$ 33