Income Taxes - Textual (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Jun. 30, 2015	Dec. 31, 2012
Income Tax Disclosure [Line Items]
Net cash payments/(refunds) for income taxes	$ (9.0)	$ 272.0	$ 139.0
State income tax benefits as a result of utilization of State of Georgia net operating loss carryforward	$ 3.5			$ 24.0
Period Of Operating Loss Carryforward	4 years
Deferred tax assets	$ 6,358.0	5,241.0
Tax Credit Carryforward, Amount	554.0
State Investment Tax Credit	188.0
Tax regulatory assets	1,600.0
Tax regulatory liabilities	187.0
Amortization of deferred investment tax credits	21.0	22.0	16.0
Unrecognized Tax Benefits	$ 433.0	170.0	7.0		$ 70.0
Significantly increase or decrease in the amount of the unrecognized tax benefits associated with a majority of Southern	12 months
Investment Tax Credit Carryforward [Member]
Income Tax Disclosure [Line Items]
Deferred tax assets	$ 742.0	480.0
Alabama Power [Member]
Income Tax Disclosure [Line Items]
Net cash payments/(refunds) for income taxes	121.0	436.0	296.0
Deferred tax assets	1,511.0	1,141.0
Tax regulatory assets	523.0
Tax regulatory liabilities	70.0
Amortization of deferred investment tax credits	8.0	8.0	8.0
Georgia Power [Member]
Income Tax Disclosure [Line Items]
Net cash payments/(refunds) for income taxes	506.0	507.0	298.0
Deferred tax assets	2,017.0	1,736.0
State Investment Tax Credit	33.0	34.0	27.0
Tax regulatory assets	683.0
Tax regulatory liabilities	105.0
Amortization of deferred investment tax credits	10.0	10.0	5.0
Federal Tax Credits	3.0
State Investment Tax Credit Carryforward	188.0
Unrecognized Tax Benefits	3.0	0.0	0.0		23.0
Gulf Power [Member]
Income Tax Disclosure [Line Items]
Net cash payments/(refunds) for income taxes	(7.0)	44.0	(11.0)
Deferred tax assets	216.0	171.0
Tax regulatory assets	61.0
Tax regulatory liabilities	3.0
Amortization of deferred investment tax credits	$ 1.0	0.0	1.4
Significantly increase or decrease in the amount of the unrecognized tax benefits associated with a majority of Southern	12 months
Mississippi Power [Member]
Income Tax Disclosure [Line Items]
Net cash payments/(refunds) for income taxes	$ (33.0)	(379.0)	(134.0)
Net operating loss carryforward	3,000.0
State income tax benefits as a result of utilization of State of Georgia net operating loss carryforward	97.0
Deferred tax assets	1,400.0	1,251.0
Tax regulatory assets	291.0
Tax regulatory liabilities	8.0
Amortization of deferred investment tax credits	1.0
Unrecognized Tax Benefits	421.0	165.0	4.0		6.0
Unrecognized Tax Benefits, Interest on Income Taxes Expense	6.0	2.0	0.0
Mississippi Power [Member] | Kemper IGCC [Member]
Income Tax Disclosure [Line Items]
Unrecognized Tax Benefits	423.0
Unrecognized Tax Benefits, Interest on Income Taxes Expense	9.0
Southern Power [Member]
Income Tax Disclosure [Line Items]
Net cash payments/(refunds) for income taxes	(518.0)	(220.0)	(226.0)
Net operating loss carryforward	225.0	247.0
Deferred tax assets	794.0	481.0
Increase (decrease) in deferred tax assets valuation allowance	87.0
Operating Loss Carryforwards In Year Three	40.0
Operating Loss Carryforwards In Year Four	185.0
Amortization of deferred investment tax credits	$ 19.0	11.0	6.0
Reduction in Tax Basis of Assets Under Option One	50.00%
Unrecognized Tax Benefits	$ 8.0	5.0	2.0		$ 3.0
Significantly increase or decrease in the amount of the unrecognized tax benefits associated with a majority of Southern	12 months
Southern Power [Member] | Operating Loss Carryforward [Member]
Income Tax Disclosure [Line Items]
Deferred tax assets	$ 8.0	9.0
Southern Power [Member] | Investment Tax Credit Carryforward [Member]
Income Tax Disclosure [Line Items]
Deferred tax assets	149.0	102.0
Southern Power [Member] | Investment Tax Credit Carryforward [Member] | Nacogdoches Biomass Generating Plant [Member]
Income Tax Disclosure [Line Items]
Tax credit carryforward	162.0	74.0	158.0
Reduction in income tax expense, investment tax credits	54.0	48.0	31.0
Deferred Tax Liability, Noncurrent [Member]
Income Tax Disclosure [Line Items]
Prior Period Reclassification Adjustment		488.0	$ 143.0
Prepaid Expense, Current [Member] | Mississippi Power [Member]
Income Tax Disclosure [Line Items]
Prior Period Reclassification Adjustment		121.0
Prepaid Expense, Current [Member] | Deferred Tax Liability, Noncurrent [Member] | Alabama Power [Member]
Income Tax Disclosure [Line Items]
Prior Period Reclassification Adjustment		20.0
Prepaid Expense, Current [Member] | Deferred Tax Liability, Noncurrent [Member] | Gulf Power [Member]
Income Tax Disclosure [Line Items]
Prior Period Reclassification Adjustment		3.0
Prepaid Expense, Current [Member] | Deferred Tax Liability, Noncurrent [Member] | Mississippi Power [Member]
Income Tax Disclosure [Line Items]
Prior Period Reclassification Adjustment		105.0
Prepaid Expense, Current [Member] | Other Noncurrent Assets [Member] | Mississippi Power [Member]
Income Tax Disclosure [Line Items]
Prior Period Reclassification Adjustment		16.0
Prepaid Expense, Current [Member] | Other Noncurrent Assets [Member] | Southern Power [Member]
Income Tax Disclosure [Line Items]
Prior Period Reclassification Adjustment		306.0
Deferred Charges Related To Income Taxes, Current [Member]
Income Tax Disclosure [Line Items]
Prior Period Reclassification Adjustment		506.0
Deferred Charges Related To Income Taxes, Current [Member] | Deferred Tax Liability, Noncurrent [Member]
Income Tax Disclosure [Line Items]
Prior Period Reclassification Adjustment		488.0
Deferred Charges Related To Income Taxes, Current [Member] | Deferred Tax Liability, Noncurrent [Member] | Georgia Power [Member]
Income Tax Disclosure [Line Items]
Prior Period Reclassification Adjustment		34.0
Deferred Charges Related To Income Taxes, Current [Member] | Other Noncurrent Assets [Member]
Income Tax Disclosure [Line Items]
Prior Period Reclassification Adjustment		18.0
Accrued Income Taxes, Current [Member] | Deferred Tax Liability, Noncurrent [Member]
Income Tax Disclosure [Line Items]
Prior Period Reclassification Adjustment		2.0
Accrued Income Taxes, Current [Member] | Deferred Tax Liability, Noncurrent [Member] | Alabama Power [Member]
Income Tax Disclosure [Line Items]
Prior Period Reclassification Adjustment		2.0
Accrued Income Taxes, Current [Member] | Deferred Tax Liability, Noncurrent [Member] | Southern Power [Member]
Income Tax Disclosure [Line Items]
Prior Period Reclassification Adjustment		$ 2.0
Georgia [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforward	697.0
State income tax benefits as a result of utilization of State of Georgia net operating loss carryforward	27.0
Mississippi [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforward	3,000.0
State income tax benefits as a result of utilization of State of Georgia net operating loss carryforward	97.0
New Mexico [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforward	133.0
State income tax benefits as a result of utilization of State of Georgia net operating loss carryforward	5.0
Florida [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforward	115.0
State income tax benefits as a result of utilization of State of Georgia net operating loss carryforward	$ 4.0