Contingencies and Regulatory Matters - Nuclear Construction Cost and Schedule (Details) - GEORGIA POWER CO - Plant Vogtle Units 3 And 4 $ in Billions	Mar. 31, 2018 USD ($)
Loss Contingencies [Line Items]
Estimated cost to complete	$ 7.3
Net investment as of March 31, 2018	(3.7)
Remaining estimate to complete	$ (3.6)