Acquisitions - Narrative (Details) $ / shares in Units, $ in Millions			3 Months Ended		6 Months Ended		36 Months Ended
	Jul. 01, 2016 USD ($)	May 09, 2016 USD ($) $ / shares	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2020	Aug. 01, 2017 MW	Dec. 31, 2016 USD ($) MW
Business Acquisition [Line Items]
Goodwill			$ 6,271		$ 6,271				$ 6,251
Revenues			5,430	$ 4,459	11,202	$ 8,451
Consolidated net income (loss) attributable to Southern Company			(1,381)	623	(723)	1,112
Construction work in progress			7,440		7,440				8,977
SOUTHERN Co GAS
Business Acquisition [Line Items]
Goodwill			5,967		5,967				5,967
Revenues			716		2,276
Consolidated net income (loss) attributable to Southern Company			49		288
Construction work in progress			779		779				496
SOUTHERN POWER CO
Business Acquisition [Line Items]
Goodwill			2		2				2
Revenues			529	373	979	688
Consolidated net income (loss) attributable to Southern Company			82	$ 89	151	$ 139
Total costs of construction					421
Construction work in progress			344		344				$ 398
SOUTHERN Co GAS
Business Acquisition [Line Items]
Aggregate purchase price	$ 8,000
Goodwill			5,967		$ 5,967
SOUTHERN Co GAS | Minimum
Business Acquisition [Line Items]
Estimated lives of intangible assets					1 year
SOUTHERN Co GAS | Maximum
Business Acquisition [Line Items]
Estimated lives of intangible assets					28 years
PowerSecure International, Inc.
Business Acquisition [Line Items]
Aggregate purchase price		$ 429
Goodwill			284		$ 284
Acquisition, share price (in dollars per share) | $ / shares		$ 18.75
PowerSecure International, Inc. | Minimum
Business Acquisition [Line Items]
Estimated lives of intangible assets					1 year
PowerSecure International, Inc. | Maximum
Business Acquisition [Line Items]
Estimated lives of intangible assets					26 years
Series of Construction Projects | SOUTHERN POWER CO
Business Acquisition [Line Items]
Construction work in progress			49		$ 49
Series of Construction Projects | Minimum | SOUTHERN POWER CO
Business Acquisition [Line Items]
Estimated future construction payments			170		170
Series of Construction Projects | Maximum | SOUTHERN POWER CO
Business Acquisition [Line Items]
Estimated future construction payments			$ 190		$ 190
Renewable Energy Systems Americas, Inc. | SOUTHERN POWER CO
Business Acquisition [Line Items]
Approx. nameplate capacity, wind (MW) | MW									3,000
Wind Generating Facility | Scenario, Forecast | SOUTHERN POWER CO
Business Acquisition [Line Items]
Project qualification for production tax credits, percentage							100.00%
Production tax credits, project qualification period							10 years
Subsequent Event | SOUTHERN POWER CO
Business Acquisition [Line Items]
Ownership percentage by parent								100.00%
Approximate Nameplate Capacity (MW) | MW								148