Income Taxes (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Income Tax Contingency [Line Items]
Operating loss carryforwards	$ 24
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits as of December 31, 2014	170
Tax positions from current periods	2
Tax positions from prior periods	231
Reductions due to settlements	(5)
Balance as of June 30, 2015	398
Tax positions impacting the effective tax rate	8		$ 10
Tax positions not impacting the effective tax rate	390		160
Kemper Igcc [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance as of June 30, 2015	390
Unrecognized tax benefit, associated interest	$ 5
Mississippi Power [Member]
Income Tax Contingency [Line Items]
Effective tax rate	19.00%	(51.10%)
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits as of December 31, 2014	$ 165
Tax positions from current periods	0
Tax positions from prior periods	230
Reductions due to settlements	(5)
Balance as of June 30, 2015	390
Tax positions impacting the effective tax rate	0
Tax positions not impacting the effective tax rate	390
Mississippi Power [Member] | Kemper Igcc [Member]
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits, Interest on Income Taxes Expense	5
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance as of June 30, 2015	390
Southern Power [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards	$ 428		$ 305
Effective tax rate	13.70%	0.30%
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits as of December 31, 2014	$ 5
Tax positions from current periods	2
Tax positions from prior periods	0
Reductions due to settlements	0
Balance as of June 30, 2015	7
Tax positions impacting the effective tax rate	7
Tax positions not impacting the effective tax rate	$ 0