Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Dec. 31, 2016
Income Tax Contingency [Line Items]
Effective tax rate	32.10%	30.20%
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	9
Tax positions from prior periods	7
Balance as of March 31, 2017	500
Tax positions impacting the effective tax rate			$ 36	$ 20
Tax positions not impacting the effective tax rate			464	464
Balance of unrecognized tax benefits	$ 484		500	484
Significantly Increase or Decrease in Amount of Unrecognized Tax Benefits	12 months
Kemper IGCC [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance as of March 31, 2017	$ 464
Balance of unrecognized tax benefits	$ 464		464
Unrecognized tax benefit, associated interest			32
Mississippi Power [Member]
Income Tax Contingency [Line Items]
Effective tax rate	(58.70%)	(850.40%)
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 March 31, 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 [Member] | Kemper IGCC [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance as of March 31, 2017	464
Balance of unrecognized tax benefits	$ 464		464
Unrecognized tax benefit, associated interest			32
Southern Power [Member]
Income Tax Contingency [Line Items]
Effective tax rate	(385.90%)	(84.00%)
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	0
Balance as of March 31, 2017	18
Tax positions impacting the effective tax rate			18
Tax positions not impacting the effective tax rate			0
Balance of unrecognized tax benefits	$ 17		18	17
Investment Tax Credit Carryforward [Member]
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