The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Amortization of Other Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Amortization associated with other intangible assets	$ 49	$ 61	$ 89
Estimated future amortization
2021	43
2022	39
2023	37
2024	35
2025	32
Southern Power
Finite-Lived Intangible Assets [Line Items]
Amortization associated with other intangible assets	20	19	25
Estimated future amortization
2021	20
2022	20
2023	20
2024	20
2025	20
Southern Company Gas
Finite-Lived Intangible Assets [Line Items]
Amortization associated with other intangible assets	19	31	52
Estimated future amortization
2021	14
2022	11
2023	9
2024	7
2025	6
Southern Company Gas \| Gas marketing services
Finite-Lived Intangible Assets [Line Items]
Amortization associated with other intangible assets	17	23	32
Southern Company Gas \| Wholesale gas services
Finite-Lived Intangible Assets [Line Items]
Amortization associated with other intangible assets	2	8	20
Operating Revenues
Finite-Lived Intangible Assets [Line Items]
Amortization associated with other intangible assets	$ 22	$ 27	$ 45