Income Taxes - NOL Carryforwards (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Operating Loss Carryforwards [Line Items]
NOL Carryforwards	$ 3,000
Net State Income Tax Benefit	203
Mississippi
Operating Loss Carryforwards [Line Items]
Net State Income Tax Benefit	112
Oklahoma
Operating Loss Carryforwards [Line Items]
Net State Income Tax Benefit	31
Georgia
Operating Loss Carryforwards [Line Items]
Net State Income Tax Benefit	25
New York
Operating Loss Carryforwards [Line Items]
Net State Income Tax Benefit	11
New York City
Operating Loss Carryforwards [Line Items]
Net State Income Tax Benefit	12
Florida
Operating Loss Carryforwards [Line Items]
Net State Income Tax Benefit	7
Other states
Operating Loss Carryforwards [Line Items]
Net State Income Tax Benefit	5
Southern Power [Member]
Operating Loss Carryforwards [Line Items]
NOL Carryforwards	1,030
Net State Income Tax Benefit	40	$ 8
Southern Power [Member] | Oklahoma
Operating Loss Carryforwards [Line Items]
NOL Carryforwards	838
Net State Income Tax Benefit	32
Southern Power [Member] | Florida
Operating Loss Carryforwards [Line Items]
NOL Carryforwards	185
Net State Income Tax Benefit	7
Southern Power [Member] | Other states
Operating Loss Carryforwards [Line Items]
NOL Carryforwards	7
Net State Income Tax Benefit	1
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
NOL Carryforwards	5,754
State and Local Jurisdiction [Member] | Mississippi
Operating Loss Carryforwards [Line Items]
NOL Carryforwards	3,448
State and Local Jurisdiction [Member] | Oklahoma
Operating Loss Carryforwards [Line Items]
NOL Carryforwards	839
State and Local Jurisdiction [Member] | Georgia
Operating Loss Carryforwards [Line Items]
NOL Carryforwards	685
State and Local Jurisdiction [Member] | New York
Operating Loss Carryforwards [Line Items]
NOL Carryforwards	229
State and Local Jurisdiction [Member] | New York City
Operating Loss Carryforwards [Line Items]
NOL Carryforwards	209
State and Local Jurisdiction [Member] | Florida
Operating Loss Carryforwards [Line Items]
NOL Carryforwards	198
State and Local Jurisdiction [Member] | Other states
Operating Loss Carryforwards [Line Items]
NOL Carryforwards	$ 146