Acquisitions and Dispositions - Pre-tax Profit (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
GULF POWER CO
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Earnings before income taxes:	$ 31	$ 61	$ 87	$ 95
Florida Plants \| SOUTHERN POWER CO
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Earnings before income taxes:	$ 14	$ 11	$ 24	$ 20

Amount before tax of income (loss) from an individually significant component disposed of or held-for-sale attributable to parent. Excludes discontinued operations.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 3A
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=84176398&loc=SL51724579-110230

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration