Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Income Tax Contingency [Line Items]
Effective tax rate	30.80%	34.30%
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	5
Balance as of March 31, 2016	438
Tax positions impacting the effective tax rate	15		$ 10
Tax positions not impacting the effective tax rate	423		423
Kemper IGCC [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance as of March 31, 2016	423
Unrecognized tax benefit, associated interest	$ 12
Mississippi Power [Member]
Income Tax Contingency [Line Items]
Effective tax rate	(838.70%)	10.00%
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
Balance as of March 31, 2016	421
Tax positions impacting the effective tax rate	(2)
Tax positions not impacting the effective tax rate	423
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, 2016	423
Unrecognized tax benefit, associated interest	12
Southern Power [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards	$ 694		$ 551
Effective tax rate	(84.00%)	25.80%
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	5
Balance as of March 31, 2016	13
Tax positions impacting the effective tax rate	13
Tax positions not impacting the effective tax rate	$ 0