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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Other Intangible Assets (Details) - USD ($) $ in Millions | Dec. 31, 2021 | Dec. 31, 2020
--- | --- | ---
Finite-Lived Intangible Assets [Line Items] |  |
Gross Carrying Amount | $ 677 | $ 740
Accumulated Amortization | (307) | (328)
Other Intangible Assets, Net | 370 | 412
Intangible assets, gross | 752 | 815
Intangible assets, net | 445 | 487
Federal Communications Commission licenses |  |
Finite-Lived Intangible Assets [Line Items] |  |
Gross Carrying Amount | 75 | 75
Accumulated Amortization | 0 | 0
Other Intangible Assets, Net | 75 | 75
Customer relationships |  |
Finite-Lived Intangible Assets [Line Items] |  |
Gross Carrying Amount | 212 | 212
Accumulated Amortization | (150) | (135)
Other Intangible Assets, Net | 62 | 77
Trade names |  |
Finite-Lived Intangible Assets [Line Items] |  |
Gross Carrying Amount | 64 | 64
Accumulated Amortization | (38) | (31)
Other Intangible Assets, Net | 26 | 33
Storage and transportation contracts |  |
Finite-Lived Intangible Assets [Line Items] |  |
Gross Carrying Amount | 0 | 64
Accumulated Amortization | 0 | (64)
Other Intangible Assets, Net | 0 | 0
PPA fair value adjustments |  |
Finite-Lived Intangible Assets [Line Items] |  |
Gross Carrying Amount | 390 | 390
Accumulated Amortization | (109) | (89)
Other Intangible Assets, Net | 281 | 301
Other |  |
Finite-Lived Intangible Assets [Line Items] |  |
Gross Carrying Amount | 11 | 10
Accumulated Amortization | (10) | (9)
Other Intangible Assets, Net | 1 | 1
Southern Power |  |
Finite-Lived Intangible Assets [Line Items] |  |
Accumulated Amortization | (109) | (89)
Southern Power | PPA fair value adjustments |  |
Finite-Lived Intangible Assets [Line Items] |  |
Gross Carrying Amount | 390 | 390
Accumulated Amortization | (109) | (89)
Other Intangible Assets, Net | 281 | 301
Southern Company Gas |  |
Finite-Lived Intangible Assets [Line Items] |  |
Gross Carrying Amount | 182 | 246
Accumulated Amortization | (145) | (195)
Other Intangible Assets, Net | 37 | 51
Intangible assets, net | 37 | 51
Southern Company Gas | Customer relationships |  |
Finite-Lived Intangible Assets [Line Items] |  |
Gross Carrying Amount | 156 | 156
Accumulated Amortization | (130) | (119)
Other Intangible Assets, Net | 26 | 37
Southern Company Gas | Trade names |  |
Finite-Lived Intangible Assets [Line Items] |  |
Gross Carrying Amount | 26 | 26
Accumulated Amortization | (15) | (12)
Other Intangible Assets, Net | 11 | 14
Southern Company Gas | Storage and transportation contracts |  |
Finite-Lived Intangible Assets [Line Items] |  |
Gross Carrying Amount | 0 | 64
Accumulated Amortization | 0 | (64)
Other Intangible Assets, Net | $ 0 | $ 0

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