Introduction - Narrative (Details)	1 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($) business_unit	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Goodwill impairment		$ 32,000,000		$ 32,000,000
SOUTHERN Co GAS
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Goodwill impairment		0	$ 0	0	$ 42,000,000
Inventory decrement		7,000,000	$ 0	$ 10,000,000	$ 0
ALABAMA POWER CO
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in ARO	$ 308,000,000
MISSISSIPPI POWER CO
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in ARO	$ 58,000,000
Disposal Group, Held-for-sale, Not Discontinued Operations | PowerSecure International, Inc.
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Goodwill impairment		$ 32,000,000
Number Of Business Units | business_unit		1