Contingencies and Regulatory Matters - Nuclear Construction Cost and Schedule (Details) - GEORGIA POWER CO - Plant Vogtle Units 3 And 4 $ in Millions	9 Months Ended
	Sep. 30, 2018 USD ($)
Loss Contingencies [Line Items]
Base project capital cost forecast	$ 8,000
Construction contingency estimate	400
Project capital cost forecast	8,400
Net investment as of June 30, 2018	(4,300)
Remaining estimate to complete	4,100
Expected capitalized costs	350
Guarantor obligations	1,700
Customer refund	$ 188