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Acquisitions and Dispositions - Southern Power Narrative (Details) $ in Millions			1 Months Ended	6 Months Ended	7 Months Ended
	Oct. 01, 2019 USD ($)	Jun. 13, 2019 USD ($) MW	Jun. 30, 2019 USD ($) MW	Jun. 30, 2019 USD ($) MW	Dec. 31, 2019 USD ($)	May 31, 2019 MW	May 04, 2019 MW	Dec. 31, 2018 USD ($)
Business Acquisition [Line Items]
Construction work in progress			$ 7,568	$ 7,568				$ 7,254
Property, plant, and equipment, subject to lien			114,867	114,867				116,914
SOUTHERN POWER CO
Business Acquisition [Line Items]
Construction work in progress			419	419				430
Property, plant, and equipment, subject to lien			14,518	14,518				$ 14,883
SOUTHERN POWER CO \| Lien
Business Acquisition [Line Items]
Property, plant, and equipment, subject to lien			545	545
SOUTHERN POWER CO \| Disposal Group, Held-for-sale, Not Discontinued Operations \| Mankato expansion \| Scenario, Forecast
Business Acquisition [Line Items]
Gain on termination fee	$ 15
SOUTHERN POWER CO \| Disposal Group, Held-for-sale, Not Discontinued Operations \| Nacogdoches Biomass-Fueled Facility
Business Acquisition [Line Items]
Approximate nameplate capacity (MW) \| MW		115
Nacogdoches biomass-fueled facility		$ 461
After tax gain		$ 88
SOUTHERN POWER CO \| Wind Generating Facility
Business Acquisition [Line Items]
Gain on sale				14
SOUTHERN POWER CO \| Series of Construction Projects
Business Acquisition [Line Items]
Construction work in progress			186	186
SOUTHERN POWER CO \| Series of Construction Projects \| Minimum
Business Acquisition [Line Items]
Estimated future construction payments			405	405
SOUTHERN POWER CO \| Series of Construction Projects \| Maximum
Business Acquisition [Line Items]
Estimated future construction payments			450	$ 450
SOUTHERN POWER CO \| Diamond State Generation Partners
Business Acquisition [Line Items]
Contributions to acquire majority interest			$ 116
SOUTHERN POWER CO \| Diamond State Generation Partners \| Scenario, Forecast
Business Acquisition [Line Items]
Contributions to acquire majority interest					$ 173
SOUTHERN POWER CO \| Mankato expansion
Business Acquisition [Line Items]
Approximate nameplate capacity (MW) \| MW			385	385		385	385