ACQUISITIONS AND DISPOSITIONS - Schedule of Pre-tax Income (Details) - Southern Power - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Plant Nacogdoches
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Earnings before income taxes		$ 13
Mankato
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Earnings before income taxes	$ 2	$ 29

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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 3A
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=109226691&loc=SL51724579-110230

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