Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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Amount of transfers into (out of) an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

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Amount of divestiture of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Introduction - Goodwill (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
Introduction - Goodwill (Details) - USD ($) $ in Millions	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Goodwill [Roll Forward]
Balance at December 31, 2017		$ 6,268		$ 6,268
Impairment				(42)
Sale of Pivotal Home Solutions				(242)
Reclassification to held for sale				(668)
Balance at June 30, 2018	$ 5,315			5,315
SOUTHERN Co GAS
Goodwill [Roll Forward]
Balance at December 31, 2017		5,967		5,967
Impairment	0	(42)	$ 0	(42)	$ 0
Sale of Pivotal Home Solutions				(242)
Reclassification to held for sale				(668)
Balance at June 30, 2018	5,015			5,015
SOUTHERN Co GAS \| Gas Distribution Operations
Goodwill [Roll Forward]
Balance at December 31, 2017		4,702		4,702
Impairment				0
Sale of Pivotal Home Solutions				0
Reclassification to held for sale				(668)
Balance at June 30, 2018	4,034			4,034
SOUTHERN Co GAS \| Gas Marketing Services
Goodwill [Roll Forward]
Balance at December 31, 2017		$ 1,265		1,265
Impairment				(42)
Sale of Pivotal Home Solutions				(242)
Reclassification to held for sale				0
Balance at June 30, 2018	$ 981			$ 981