Acquisitions and Dispositions - Southern Power Narrative (Details) $ in Millions	14 Months Ended
	Dec. 31, 2019 USD ($) MW	May 31, 2019 MW	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Business Acquisition [Line Items]
Construction work in progress			$ 7,598	$ 7,254
Property, plant, and equipment, subject to lien			114,096	116,914
SOUTHERN POWER CO
Business Acquisition [Line Items]
Construction work in progress			409	430
Property, plant, and equipment, subject to lien			15,104	$ 14,883
SOUTHERN POWER CO | Lien
Business Acquisition [Line Items]
Property, plant, and equipment, subject to lien			538
SOUTHERN POWER CO | Disposal Group, Held-for-sale, Not Discontinued Operations | Mankato expansion | Scenario, Forecast
Business Acquisition [Line Items]
Proceeds from divestiture of businesses, net of cash divested	$ 650
Approximate nameplate capacity (MW) | MW	385
SOUTHERN POWER CO | Disposal Group, Held-for-sale, Not Discontinued Operations | Nacogdoches Biomass-Fueled Facility | Subsequent Event | Scenario, Forecast
Business Acquisition [Line Items]
Nacogdoches biomass-fueled facility	$ 460
SOUTHERN POWER CO | Wind Generating Facility
Business Acquisition [Line Items]
Equipment marketed for sale			53
SOUTHERN POWER CO | Series of Construction Projects
Business Acquisition [Line Items]
Construction work in progress			347
SOUTHERN POWER CO | Series of Construction Projects | Minimum
Business Acquisition [Line Items]
Estimated future construction payments			575
SOUTHERN POWER CO | Series of Construction Projects | Maximum
Business Acquisition [Line Items]
Estimated future construction payments			$ 640
SOUTHERN POWER CO | Mankato expansion | Scenario, Forecast
Business Acquisition [Line Items]
Approximate nameplate capacity (MW) | MW		385