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, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2010
Accounting Policies [Line Items]
Deferred income tax assets		$ 9,495		$ 8,424	$ 9,495		$ 9,495
Maximum
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 CO
Accounting Policies [Line Items]
Deferred income tax assets		1,544		$ 1,028	1,544		1,544
ALABAMA POWER CO | Maximum
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%
GEORGIA POWER CO
Accounting Policies [Line Items]
Federal tax credits				$ 87
Deferred income tax assets		2,382		$ 1,886	2,382		2,382
GEORGIA POWER CO | Maximum
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 CO
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		$ 275	244		244
GULF POWER CO | Minimum
Accounting Policies [Line Items]
Projected fuel cost over or under recovery threshold, as a percentage of projected fuel revenue				10.00%
GULF POWER CO | Maximum
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 CO
Accounting Policies [Line Items]
Percentage of wholesale customers to operating revenue				19.30%
Period of contract cancellation notices of wholesale customers				10 years
Deferred income tax assets		1,022		$ 1,173	1,022		1,022
Grants received from Department of Energy							382
MISSISSIPPI POWER CO | Maximum
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 CO | Kemper IGCC
Accounting Policies [Line Items]
Grants expected to be received from Department of Energy				$ 2				$ 270
Grants received from Department of Energy	$ 137						245
SOUTHERN POWER CO
Accounting Policies [Line Items]
Deferred income tax assets		2,937		$ 2,693	$ 2,937		2,937
Reduction in tax basis of assets				50.00%
SOUTHERN POWER CO | Sales Revenue, Goods, Net | GEORGIA POWER CO | Customer Concentration Risk
Accounting Policies [Line Items]
Maximum revenue from a single customer or industry (more than)				11.30%	16.50%	15.80%
SOUTHERN POWER CO | Sales Revenue, Goods, Net | Duke Energy Corporation | Customer Concentration Risk
Accounting Policies [Line Items]
Maximum revenue from a single customer or industry (more than)				6.70%	7.80%	8.20%
SOUTHERN POWER CO | Sales Revenue, Goods, Net | Morgan Stanley Capital Group | Customer Concentration Risk
Accounting Policies [Line Items]
Maximum revenue from a single customer or industry (more than)				4.50%
SOUTHERN POWER CO | Sales Revenue, Goods, Net | San Diego Gas & Electric Company | Customer Concentration Risk
Accounting Policies [Line Items]
Maximum revenue from a single customer or industry (more than)					5.70%
SOUTHERN POWER CO | Sales Revenue, Goods, Net | Florida Power & Light Company | Customer Concentration Risk
Accounting Policies [Line Items]
Maximum revenue from a single customer or industry (more than)						10.70%
SOUTHERN Co GAS
Accounting Policies [Line Items]
Deferred income tax assets		598		$ 849	$ 598		$ 598
Period for collection of revenue prior to billings				24 months
Excise taxes collected		32		$ 100
SOUTHERN Co GAS | Maximum
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 Co GAS | Predecessor
Accounting Policies [Line Items]
Excise taxes collected			$ 57			$ 103
Investment Tax And Other Credit Carryforward | GEORGIA POWER CO
Accounting Policies [Line Items]
Deferred income tax assets				$ 495
Included In Operating Expenses | SOUTHERN Co GAS
Accounting Policies [Line Items]
Excise taxes collected		$ 31		$ 98
Included In Operating Expenses | SOUTHERN Co GAS | Predecessor
Accounting Policies [Line Items]
Excise taxes collected			$ 56			$ 101