Regulatory Matters - Nuclear Construction Joint Owner Contracts (Details) - Georgia Power - Plant Vogtle Units 3 And 4	12 Months Ended
	Dec. 31, 2018 USD ($) MW	Dec. 31, 2015 USD ($)	Aug. 31, 2018
Loss Contingencies [Line Items]
Ownership interest percentage required for voting for continuing construction	90.00%		90.00%
Total project capital cost forecast	$ 8,400,000,000
Additional construction capital costs		$ 3,300,000,000
Additional qualifying construction costs	$ 2,100,000,000
Percent of remaining share of total construction costs	100.00%
Percentage of cost savings	60.70%
Nonqualifying construction costs threshold	$ 100,000
Percentage of costs disallowed for recovery	6.00%
Costs disallowed for recovery, period	6 months
Public utilities extension project schedule term	1 year
Percentage of approval required to change primary construction contractor	90.00%
Percentage of approval required for material amendments	67.00%
Continued construction voted in favor, period	30 days
Percentage of continued construction voted in favor	50.00%
Share of plants (mw) | MW	206
Purchase rights to PTCs, period	30 days
Aggregate purchase price of PTCs	$ 300,000,000
Maximum aggregate funding	$ 250,000,000
Vogtle Owners
Loss Contingencies [Line Items]
Percentage of cost savings	39.30%
Category I
Loss Contingencies [Line Items]
Additional construction capital costs	$ 800,000,000
Category II
Loss Contingencies [Line Items]
Percentage of construction costs responsible to pay	55.70%
Category II | Vogtle Owners
Loss Contingencies [Line Items]
Percentage of construction costs responsible to pay	44.30%
Category II | Minimum
Loss Contingencies [Line Items]
Additional construction capital costs	$ 80,000,000
Additional qualifying construction costs	800,000,000
Category II | Maximum
Loss Contingencies [Line Items]
Additional qualifying construction costs	$ 1,600,000,000
Category III
Loss Contingencies [Line Items]
Percentage of construction costs responsible to pay	65.70%
Category III | Vogtle Owners
Loss Contingencies [Line Items]
Percentage of construction costs responsible to pay	34.30%
Category III | Minimum
Loss Contingencies [Line Items]
Additional construction capital costs	$ 100,000,000
Additional qualifying construction costs	1,600,000,000
Category III | Maximum
Loss Contingencies [Line Items]
Additional qualifying construction costs	$ 2,100,000,000