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PROPERTY, PLANT, AND EQUIPMENT - Depreciation and Amortization (Narrative) (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2021 | Dec. 31, 2020
Property, Plant and Equipment [Line Items] |  |
Accumulated depreciation | $ 34,079 | $ 32,397
Utility plant in service |  |
Property, Plant and Equipment [Line Items] |  |
Accumulated depreciation | 33,100 | 31,600
Other plant in service |  |
Property, Plant and Equipment [Line Items] |  |
Accumulated depreciation | $ 930 | 817
Other plant in service | Maximum |  |
Property, Plant and Equipment [Line Items] |  |
Depreciation period of original cost | 37 years |
Southern Company Gas |  |
Property, Plant and Equipment [Line Items] |  |
Accumulated depreciation | $ 5,067 | 4,821
Southern Company Gas | Utility plant in service |  |
Property, Plant and Equipment [Line Items] |  |
Accumulated depreciation | 4,800 | 4,600
Southern Company Gas | Other plant in service |  |
Property, Plant and Equipment [Line Items] |  |
Accumulated depreciation | $ 219 | $ 195
Southern Company Gas | Transportation equipment | Minimum |  |
Property, Plant and Equipment [Line Items] |  |
Depreciation period of original cost | 5 years |
Southern Company Gas | Transportation equipment | Maximum |  |
Property, Plant and Equipment [Line Items] |  |
Depreciation period of original cost | 12 years |
Southern Company Gas | Storage facilities | Minimum |  |
Property, Plant and Equipment [Line Items] |  |
Depreciation period of original cost | 30 years |
Southern Company Gas | Storage facilities | Maximum |  |
Property, Plant and Equipment [Line Items] |  |
Depreciation period of original cost | 75 years |
Southern Company Gas | Other assets | Maximum |  |
Property, Plant and Equipment [Line Items] |  |
Depreciation period of original cost | 75 years |

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- Definition Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.14) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition Useful life of other property, plant and equipment (PPE) owned by public utility, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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