Summary of Significant Accounting Policies - Government Grants, Revenue, Taxes, Concentration Risk (Details) - USD ($) $ in Millions		6 Months Ended		12 Months Ended			84 Months Ended
	Apr. 08, 2016	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016	Dec. 31, 2010
Accounting Policies [Line Items]
Deferred income tax assets		$ 9,495		$ 9,495	$ 6,683		$ 9,495
Maximum [Member]
Accounting Policies [Line Items]
Maximum revenue from a single customer or industry (more than)				10.00%
Maximum percentage of uncollectible accounts (less than)				1.00%
Gulf Power [Member]
Accounting Policies [Line Items]
Projected fuel cost over or under recovery threshold, as a percentage of projected fuel revenue				10.00%
Deferred income tax assets		244		$ 244	216		244
Gulf Power [Member] | Maximum [Member]
Accounting Policies [Line Items]
Maximum revenue from a single customer or industry (more than)				10.00%
Maximum percentage of uncollectible accounts (less than)				1.00%
Gulf Power [Member] | Minimum [Member]
Accounting Policies [Line Items]
Projected fuel cost over or under recovery threshold, as a percentage of projected fuel revenue				10.00%
Southern Company Gas [Member]
Accounting Policies [Line Items]
Period for collection of revenue prior to billings				24 months
Southern Company Gas [Member] | Maximum [Member]
Accounting Policies [Line Items]
Maximum revenue from a single customer or industry (more than)				10.00%
Maximum percentage of uncollectible accounts (less than)				1.00%
Southern Company Gas [Member] | Successor [Member]
Accounting Policies [Line Items]
Deferred income tax assets		598		$ 598			598
Excise Taxes Collected		32
Southern Company Gas [Member] | Predecessor [Member]
Accounting Policies [Line Items]
Deferred income tax assets					438
Excise Taxes Collected			$ 57		103	$ 133
Mississippi Power [Member]
Accounting Policies [Line Items]
Percentage Of Wholesale Customers To Operating Revenue				19.80%
Period Of Contract Cancellation Notices Of Wholesale Customers				10 years
Deferred income tax assets		1,024		$ 1,024	1,400		1,024
Grants received from Department of Energy							382
Mississippi Power [Member] | Maximum [Member]
Accounting Policies [Line Items]
Maximum revenue from a single customer or industry (more than)				10.00%
Maximum percentage of uncollectible accounts (less than)				1.00%
Mississippi Power [Member] | Kemper IGCC [Member]
Accounting Policies [Line Items]
Grants expected to be received from Department of Energy		25		$ 25			25	$ 270
Grants received from Department of Energy	$ 137			140			245
Southern Power [Member]
Accounting Policies [Line Items]
Deferred income tax assets		2,937		$ 2,937	$ 794		2,937
Reduction in tax basis of assets				50.00%
Southern Power [Member] | Sales Revenue, Goods, Net [Member] | Georgia Power [Member] | Customer Concentration Risk [Member]
Accounting Policies [Line Items]
Maximum revenue from a single customer or industry (more than)				16.50%	15.80%	10.10%
Southern Power [Member] | Sales Revenue, Goods, Net [Member] | Duke Energy Corporation | Customer Concentration Risk [Member]
Accounting Policies [Line Items]
Maximum revenue from a single customer or industry (more than)				7.80%	8.20%	9.10%
Southern Power [Member] | Sales Revenue, Goods, Net [Member] | San Diego Gas & Electric Company | Customer Concentration Risk [Member]
Accounting Policies [Line Items]
Maximum revenue from a single customer or industry (more than)				5.70%	6.10%	2.90%
Southern Power [Member] | Sales Revenue, Goods, Net [Member] | FPL | Customer Concentration Risk [Member]
Accounting Policies [Line Items]
Maximum revenue from a single customer or industry (more than)				0.00%	10.70%	9.70%
Georgia Power [Member]
Accounting Policies [Line Items]
Federal tax credits				$ 83
Deferred income tax assets		2,382		$ 2,382	$ 2,077		2,382
Georgia Power [Member] | Maximum [Member]
Accounting Policies [Line Items]
Maximum revenue from a single customer or industry (more than)				10.00%
Maximum percentage of uncollectible accounts (less than)				1.00%
Alabama Power [Member]
Accounting Policies [Line Items]
Deferred income tax assets		1,544		$ 1,544	1,511		1,544
Alabama Power [Member] | Maximum [Member]
Accounting Policies [Line Items]
Maximum revenue from a single customer or industry (more than)				10.00%
Maximum percentage of uncollectible accounts (less than)				1.00%
Investment Tax And Other Credit Carryforward [Member] | Georgia Power [Member]
Accounting Policies [Line Items]
Deferred income tax assets		345		$ 345			$ 345
Included In Operating Expenses [Member] | Southern Company Gas [Member] | Successor [Member]
Accounting Policies [Line Items]
Excise Taxes Collected		$ 31
Included In Operating Expenses [Member] | Southern Company Gas [Member] | Predecessor [Member]
Accounting Policies [Line Items]
Excise Taxes Collected			$ 56		$ 101	$ 130