Income Taxes - Textual (Details) - USD ($)	6 Months Ended		12 Months Ended
	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Line Items]
Net cash payments/(refunds) for income taxes			$ (148,000,000)	$ (9,000,000)	$ 272,000,000
Tax regulatory assets	$ 1,600,000,000		1,600,000,000
Tax regulatory liabilities	219,000,000		219,000,000
Amortization of deferred investment tax credits			22,000,000	21,000,000	22,000,000
Tax credit carryforward	1,800,000,000		1,800,000,000
State investment tax credit			202,000,000
Tax positions not impacting the effective tax rate	464,000,000		$ 464,000,000	423,000,000	160,000,000
Significantly increase or decrease in the amount of the unrecognized tax benefits associated with a majority of Southern			12 months
Unrecognized tax benefits	484,000,000		$ 484,000,000	433,000,000	170,000,000	$ 7,000,000
Net operating loss carryforward	3,000,000,000		3,000,000,000
State income tax benefits as a result of utilization of State of Georgia net operating loss carryforward	203,000,000		203,000,000
Deferred tax assets	9,495,000,000		9,495,000,000	6,683,000,000
Investment Tax Credit Carryforward [Member]
Income Tax Disclosure [Line Items]
Deferred tax assets	1,974,000,000		1,974,000,000	770,000,000
Mississippi Power [Member]
Income Tax Disclosure [Line Items]
Net cash payments/(refunds) for income taxes			(97,000,000)	(33,000,000)	(379,000,000)
Tax regulatory assets	362,000,000		362,000,000
Tax regulatory liabilities	7,000,000		7,000,000
Amortization of deferred investment tax credits			1,000,000	1,000,000	1,000,000
Tax positions not impacting the effective tax rate	464,000,000		464,000,000	423,000,000	161,000,000
Unrecognized tax benefits	465,000,000		465,000,000	421,000,000	165,000,000	4,000,000
Interest accrued during the period			15,000,000	10,000,000	2,000,000
Net operating loss carryforward	3,000,000,000		3,000,000,000
State income tax benefits as a result of utilization of State of Georgia net operating loss carryforward	112,000,000		112,000,000
Deferred tax assets	1,024,000,000		1,024,000,000	1,400,000,000
Mississippi Power [Member] | Kemper IGCC [Member]
Income Tax Disclosure [Line Items]
Unrecognized tax benefits	464,000,000		464,000,000
Interest accrued during the period			28,000,000
Alabama Power [Member]
Income Tax Disclosure [Line Items]
Net cash payments/(refunds) for income taxes			(108,000,000)	121,000,000	436,000,000
Tax regulatory assets	526,000,000		526,000,000
Tax regulatory liabilities	65,000,000		65,000,000
Amortization of deferred investment tax credits			8,000,000	8,000,000	8,000,000
Deferred tax assets	1,544,000,000		1,544,000,000	1,511,000,000
Georgia Power [Member]
Income Tax Disclosure [Line Items]
Net cash payments/(refunds) for income taxes			170,000,000	506,000,000	507,000,000
Tax regulatory assets	681,000,000		681,000,000
Tax regulatory liabilities	121,000,000		121,000,000
Amortization of deferred investment tax credits			10,000,000	10,000,000	10,000,000
State investment tax credit			42,000,000	33,000,000	34,000,000
Federal tax credits			83,000,000
State investment tax credit carryforward			201,000,000
Deferred tax assets	2,382,000,000		2,382,000,000	2,077,000,000
Gulf Power [Member]
Income Tax Disclosure [Line Items]
Net cash payments/(refunds) for income taxes			21,000,000	(7,000,000)	44,000,000
Tax regulatory assets	58,000,000		58,000,000
Tax regulatory liabilities	2,000,000		$ 2,000,000
Significantly increase or decrease in the amount of the unrecognized tax benefits associated with a majority of Southern			12 months
Deferred tax assets	244,000,000		$ 244,000,000	216,000,000
Southern Power [Member]
Income Tax Disclosure [Line Items]
Net cash payments/(refunds) for income taxes			116,000,000	(518,000,000)	(220,000,000)
Amortization of deferred investment tax credits			$ 37,000,000	19,000,000	11,000,000
Reduction in tax basis of assets			50.00%
Significantly increase or decrease in the amount of the unrecognized tax benefits associated with a majority of Southern			12 months
Unrecognized tax benefits	17,000,000		$ 17,000,000	8,000,000	5,000,000	$ 2,000,000
Net operating loss carryforward	1,030,000,000		1,030,000,000
State income tax benefits as a result of utilization of State of Georgia net operating loss carryforward	40,000,000		40,000,000	8,000,000
Deferred tax assets	2,937,000,000		2,937,000,000	794,000,000
Southern Power [Member] | Production Tax Credit Carryforward [Member]
Income Tax Disclosure [Line Items]
Effective Income Tax Rate Reconciliation, Tax Credit, Production, Amount			42,000,000	1,000,000
Southern Power [Member] | Investment Tax Credit Carryforward [Member]
Income Tax Disclosure [Line Items]
Deferred tax assets	292,000,000		292,000,000	149,000,000
Southern Power [Member] | Investment Tax Credit Carryforward [Member] | Nacogdoches Biomass Generating Plant [Member]
Income Tax Disclosure [Line Items]
Tax credit carryforward				162,000,000	74,000,000
Reduction in income tax expense, investment tax credits			173,000,000	54,000,000	48,000,000
Florida
Income Tax Disclosure [Line Items]
State income tax benefits as a result of utilization of State of Georgia net operating loss carryforward	7,000,000		7,000,000
Florida | Southern Power [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforward	185,000,000		185,000,000
State income tax benefits as a result of utilization of State of Georgia net operating loss carryforward	7,000,000		7,000,000
General Business Tax Credit Carryforward [Member] | Southern Power [Member]
Income Tax Disclosure [Line Items]
Tax credit carryforward	1,700,000,000		1,700,000,000
Investment Tax Credit Carryforward [Member]
Income Tax Disclosure [Line Items]
Tax positions not impacting the effective tax rate	92,000,000		92,000,000
Investment Tax Credit Carryforward [Member] | Southern Power [Member]
Income Tax Disclosure [Line Items]
Tax positions not impacting the effective tax rate	92,000,000		92,000,000
Federal [Member] | Southern Power [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforward	2,800,000,000		2,800,000,000
State [Member] | Southern Power [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforward	1,000,000,000		1,000,000,000	225,000,000
Tax Year 2016 [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforward	2,800,000,000		2,800,000,000
Successor [Member] | Southern Company Gas [Member]
Income Tax Disclosure [Line Items]
Net cash payments/(refunds) for income taxes	23,000,000
Tax regulatory liabilities	22,000,000		22,000,000
Amortization of deferred investment tax credits	1,000,000
Unrecognized tax benefits	0		0
Deferred tax assets	598,000,000		598,000,000
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	$ 0		$ 0
Predecessor [Member] | Southern Company Gas [Member]
Income Tax Disclosure [Line Items]
Net cash payments/(refunds) for income taxes		$ (100,000,000)		(26,000,000)	422,000,000
Amortization of deferred investment tax credits		1,000,000		2,000,000	2,000,000
Unrecognized tax benefits		$ 0		0	$ 0
Deferred tax assets				$ 438,000,000