Income Taxes (Details)	1 Months Ended		3 Months Ended				6 Months Ended
	Apr. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2018 operating_facility	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($) operating_facility	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) operating_facility	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Income Tax Contingency [Line Items]
Effective tax rate							(3.20%)	(28.60%)
Increase in effective tax rate due to loss on Kemper IGCC							$ 3,100,000,000
Income taxes (benefit)					$ (139,000,000)	$ (587,000,000)	(25,000,000)	$ (273,000,000)
Unrecognized tax benefits					0		$ 0
Significantly increase (decrease) in amount of unrecognized tax benefits							12 months
ALABAMA POWER CO
Income Tax Contingency [Line Items]
Effective tax rate							22.80%	40.20%
Income taxes (benefit)					64,000,000	151,000,000	$ 145,000,000	$ 277,000,000
GEORGIA POWER CO
Income Tax Contingency [Line Items]
Effective tax rate							(53.50%)	36.60%
Income taxes (benefit)					(143,000,000)	199,000,000	$ (50,000,000)	$ 355,000,000
GEORGIA POWER CO | Plant Vogtle Units 3 And 4
Income Tax Contingency [Line Items]
Estimated project costs							$ 1,100,000,000
GULF POWER CO
Income Tax Contingency [Line Items]
Effective tax rate							3.30%	39.80%
Income taxes (benefit)					(11,000,000)	24,000,000	$ 3,000,000	$ 38,000,000
MISSISSIPPI POWER CO
Income Tax Contingency [Line Items]
Effective tax rate							18.70%	(30.50%)
Increase in effective tax rate due to loss on Kemper IGCC							$ 3,100,000,000
Income taxes (benefit)					13,000,000	(881,000,000)	$ 9,000,000	$ (908,000,000)
SOUTHERN Co GAS
Income Tax Contingency [Line Items]
Effective tax rate							39.10%	38.50%
Income taxes (benefit)					55,000,000	31,000,000	$ 159,000,000	$ 180,000,000
SOUTHERN POWER CO
Income Tax Contingency [Line Items]
Effective tax rate							(1386.50%)	(114.70%)
Income taxes (benefit)	$ (4,000,000)	$ (50,000,000)			(73,000,000)	$ (38,000,000)	$ (172,000,000)	$ (90,000,000)
SOUTHERN POWER CO | Florida Plants | Disposal Group, Held-for-sale, Not Discontinued Operations
Income Tax Contingency [Line Items]
Pre-tax impairment charge					$ 119,000,000		$ 119,000,000
Number of natural gas-fired operating facilities disposed | operating_facility					2		2
Investment Tax Credit Carryforward
Income Tax Contingency [Line Items]
Tax credit carryforward, amount					$ 2,300,000,000		$ 2,300,000,000		$ 2,100,000,000
Scenario, Forecast | SOUTHERN POWER CO
Income Tax Contingency [Line Items]
Income taxes (benefit)				$ (10,000,000)
Number of operating wind facilities | operating_facility			8