Property, Plant, and Equipment - Additional Information (Narrative) (Details)	12 Months Ended
	Dec. 31, 2018
Alabama Power
Property, Plant and Equipment [Line Items]
Period to amortize costs	18 months
Plant Vogtle Units 1 and 2 | Georgia Power
Property, Plant and Equipment [Line Items]
Unit operating cycle (term)	18 months
Plant Hatch Units 1 and 2 | Georgia Power
Property, Plant and Equipment [Line Items]
Unit operating cycle (term)	24 months