Acquisitions and Dispositions - Pre-tax Profit (Details) - USD ($) $ in Millions	3 Months Ended		5 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Jun. 13, 2019	Sep. 30, 2019	Sep. 30, 2018
GULF POWER CO
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Earnings before income taxes	$ 0	$ 59		$ 0	$ 146
SOUTHERN POWER CO | Florida Plants
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Earnings before income taxes	0	18		$ 0	40
SOUTHERN POWER CO | Plant Nacogdoches
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Earnings before income taxes	$ 0	$ 7	$ 16		$ 20