Income Taxes - Narrative (Details)	1 Months Ended		3 Months Ended	12 Months Ended
	Sep. 30, 2018 USD ($) operating_facility	Sep. 30, 2017 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Income Tax Disclosure [Line Items]
Deferred income tax assets			$ 9,048,000,000	$ 9,048,000,000	$ 8,205,000,000
Income tax benefit				(449,000,000)	(142,000,000)	$ (951,000,000)
Unrecognized tax benefits			0	$ 0	18,000,000	484,000,000	$ 433,000,000
Significantly increase or decrease in the amount of the unrecognized tax benefits associated with a majority of Southern				12 months
Decrease in unrecognized tax benefits from prior periods				$ 18,000,000	196,000,000	15,000,000
ITC and PTC carryforward
Income Tax Disclosure [Line Items]
Deferred income tax assets			2,730,000,000	2,730,000,000	2,414,000,000
Georgia Power
Income Tax Disclosure [Line Items]
Deferred income tax assets			3,078,000,000	3,078,000,000	1,850,000,000
Income tax benefit				(214,000,000)	(830,000,000)	(780,000,000)
State investment tax credit carryforward				341,000,000
Georgia Power | ITC and PTC carryforward
Income Tax Disclosure [Line Items]
Deferred income tax assets			430,000,000	430,000,000	403,000,000
Southern Power
Income Tax Disclosure [Line Items]
Deferred income tax assets			2,631,000,000	$ 2,631,000,000	2,700,000,000
Reduction in tax basis of assets (percent)				50.00%
Number of wind facilities | operating_facility	8
Income tax benefit			(75,000,000)	$ 164,000,000	939,000,000	195,000,000
Unrecognized tax benefits			0	0	0	17,000,000	8,000,000
Decrease in unrecognized tax benefits from prior periods				0	17,000,000	8,000,000
Southern Power | ITCs and other credits carryforward
Income Tax Disclosure [Line Items]
Reduction in income tax expense, investment tax credits				5,000,000	0	0
Southern Power | ITC and PTC carryforward
Income Tax Disclosure [Line Items]
Deferred income tax assets			2,128,000,000	2,128,000,000	2,002,000,000
Southern Power | ITC and PTC carryforward | Nacogdoches Biomass Generating Plant
Income Tax Disclosure [Line Items]
Reduction in income tax expense, investment tax credits				1,000,000	18,000,000	173,000,000
Southern Power | Production Tax Credit Carryforward
Income Tax Disclosure [Line Items]
Effective income tax rate reconciliation, tax credit, production, amount				141,000,000	139,000,000	50,000,000
Mississippi Power
Income Tax Disclosure [Line Items]
Deferred income tax assets			515,000,000	515,000,000	1,103,000,000
Income tax benefit				102,000,000	532,000,000	104,000,000
Unrecognized tax benefits			0	0	0	465,000,000	$ 421,000,000
Decrease in unrecognized tax benefits from prior periods				0	177,000,000	0
Mississippi Power | Kemper IGCC
Income Tax Disclosure [Line Items]
Unrecognized tax benefits		$ 176,000,000
Decrease in unrecognized tax benefits from prior periods		$ 36,000,000
Mississippi Power | ITC and PTC carryforward
Income Tax Disclosure [Line Items]
Deferred income tax assets			0	0	0
State and Local Jurisdiction | Georgia Power
Income Tax Disclosure [Line Items]
Valuation allowance			33,000,000	33,000,000
State and Local Jurisdiction | Georgia Power | ITCs and other credits carryforward
Income Tax Disclosure [Line Items]
Reduction in income tax expense, investment tax credits				21,000,000	37,000,000	31,000,000
State and Local Jurisdiction | Southern Power
Income Tax Disclosure [Line Items]
Income tax benefit	$ 65,000,000
State and Local Jurisdiction | Southern Power | ITCs and other credits carryforward
Income Tax Disclosure [Line Items]
Reduction in income tax expense, investment tax credits					32,000,000	7,000,000
Deferred Charges Related To Income Taxes, Current | Other Noncurrent Assets | Southern Power | Unrealized Tax Credits
Income Tax Disclosure [Line Items]
Deferred income tax assets			128,000,000	128,000,000	$ 316,000,000	$ 1,130,000,000
Mississippi | State and Local Jurisdiction | Mississippi Power
Income Tax Disclosure [Line Items]
Operating loss carryforwards, valuation allowance			32,000,000	32,000,000
Oklahoma | State and Local Jurisdiction | Southern Power
Income Tax Disclosure [Line Items]
Operating loss carryforwards, valuation allowance			9,000,000	9,000,000
Florida | State and Local Jurisdiction | Southern Power
Income Tax Disclosure [Line Items]
Operating loss carryforwards, valuation allowance			$ 11,000,000	$ 11,000,000