Income Taxes (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Income Tax Contingency [Line Items]
Operating loss carryforwards	$ 165		$ 188
Effective tax rate	29.10%	33.50%
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits as of December 31, 2015	$ 433
Tax positions from current periods	12
Tax positions from prior periods	13
Balance as of September 30, 2016	458
Tax positions impacting the effective tax rate	20		10
Tax positions not impacting the effective tax rate	438		423
Kemper IGCC [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance as of September 30, 2016	438
Unrecognized tax benefit, associated interest	$ 24
Mississippi Power [Member]
Income Tax Contingency [Line Items]
Effective tax rate	(276.20%)	(20.90%)
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits as of December 31, 2015	$ 421
Tax positions from current periods	0
Tax positions from prior periods	18
Balance as of September 30, 2016	439
Tax positions impacting the effective tax rate	1
Tax positions not impacting the effective tax rate	438
Mississippi Power [Member] | Kemper IGCC [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance as of September 30, 2016	438
Unrecognized tax benefit, associated interest	$ 24
Southern Power [Member]
Income Tax Contingency [Line Items]
Effective tax rate	(88.90%)	6.90%
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits as of December 31, 2015	$ 8
Tax positions from current periods	12
Tax positions from prior periods	(1)
Balance as of September 30, 2016	19
Tax positions impacting the effective tax rate	19
Tax positions not impacting the effective tax rate	0
Investment Tax Credit Carryforward [Member]
Income Tax Contingency [Line Items]
Tax credit carryforward	1,200		554
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Tax positions not impacting the effective tax rate	94
General Business Tax Credit Carryforward [Member]
Income Tax Contingency [Line Items]
Tax credit carryforward	$ 26		$ 1