Income Taxes (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Dec. 31, 2016
Income Tax Contingency [Line Items]
Deferred tax assets, valuation allowance			$ 81	$ 21
Effective tax rate	(28.60%)	29.40%
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits as of December 31, 2016	$ 484
Tax positions from current periods	10
Tax positions from prior periods	7
Balance as of June 30, 2017	501
Tax positions impacting the effective tax rate			37	20
Tax positions not impacting the effective tax rate			464	464
Balance of unrecognized tax benefits	$ 484		501	484
Significantly increase (decrease) in amount of unrecognized tax benefits	12 months
Kemper IGCC
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance as of June 30, 2017	$ 464
Balance of unrecognized tax benefits	$ 464		464
Unrecognized tax benefit, associated interest			36
SOUTHERN Co GAS
Income Tax Contingency [Line Items]
Deferred tax assets, valuation allowance			19
MISSISSIPPI POWER CO
Income Tax Contingency [Line Items]
Deferred tax assets, valuation allowance			46
Effective tax rate	(30.50%)	(208.10%)
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits as of December 31, 2016	$ 465
Tax positions from current periods	3
Tax positions from prior periods	0
Balance as of June 30, 2017	468
Tax positions impacting the effective tax rate			4
Tax positions not impacting the effective tax rate			464
Balance of unrecognized tax benefits	465		468	465
MISSISSIPPI POWER CO | Kemper IGCC
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance as of June 30, 2017	464
Balance of unrecognized tax benefits	$ 464		464
Unrecognized tax benefit, associated interest			36
SOUTHERN POWER CO
Income Tax Contingency [Line Items]
Effective tax rate	(114.70%)	(74.00%)
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits as of December 31, 2016	$ 17
Tax positions from current periods	1
Tax positions from prior periods	1
Balance as of June 30, 2017	19
Tax positions impacting the effective tax rate			19
Tax positions not impacting the effective tax rate			0
Balance of unrecognized tax benefits	$ 17		19	17
Investment Tax Credit Carryforward
Income Tax Contingency [Line Items]
Tax credit carryforward, amount			1,900	$ 1,800
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Tax positions not impacting the effective tax rate			98
Federal
Income Tax Contingency [Line Items]
Deferred tax assets, valuation allowance			18
Federal | SOUTHERN Co GAS
Income Tax Contingency [Line Items]
Deferred tax assets, valuation allowance			18
Federal | MISSISSIPPI POWER CO
Income Tax Contingency [Line Items]
Deferred tax assets, valuation allowance			0
State (net of federal benefit)
Income Tax Contingency [Line Items]
Deferred tax assets, valuation allowance			63
State (net of federal benefit) | SOUTHERN Co GAS
Income Tax Contingency [Line Items]
Deferred tax assets, valuation allowance			1
State (net of federal benefit) | MISSISSIPPI POWER CO
Income Tax Contingency [Line Items]
Deferred tax assets, valuation allowance			$ 46