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Asset Retirement Obligations: | 12 Months Ended
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Dec. 31, 2023
Asset Retirement Obligation Disclosure [Abstract] |
Asset Retirement Obligations | (7) ASSET RETIREMENT OBLIGATIONS We have identified legal obligations related to reclamation of mining sites; removal of fuel tanks, transformers containing polychlorinated biphenyls, an evaporation pond; and reclamation of wind turbine sites at our Electric Utilities segment. In addition, we have identified legal obligations related to retirement of gas pipelines, wells and compressor stations at our Gas Utilities and removal of asbestos at our Utilities. We periodically review and update estimated costs related to these AROs. The actual cost may vary from estimates due to regulatory requirements, changes in technology and increased labor, materials and equipment costs. The following tables present the details of AROs which are included on the accompanying Consolidated Balance Sheets in Other deferred credits and other liabilities (in millions):
| December 31, 2022 |  | Liabilities Incurred |  | Liabilities Settled |  | Accretion |  | Revisions to Prior Estimates |  | December 31, 2023 |
Electric Utilities | $ | 27.6 |  | $ | — |  | $ | — |  | $ | 1.2 |  | $ | (0.1 | ) | $ | 28.7 |
Gas Utilities (a) |  | 61.3 |  |  | 6.7 |  |  | — |  |  | 2.3 |  |  | (2.8 | ) |  | 67.5 |
Total | $ | 88.9 |  | $ | 6.7 |  | $ | — |  | $ | 3.5 |  | $ | (2.9 | ) | $ | 96.2 |
| December 31, 2021 |  | Liabilities Incurred |  | Liabilities Settled |  | Accretion |  | Revisions to Prior Estimates |  | December 31, 2022 |
Electric Utilities | $ | 30.1 |  | $ | — |  | $ | (3.0 | ) | $ | 1.4 |  | $ | (0.9 | ) | $ | 27.6 |
Gas Utilities (a) |  | 45.5 |  |  | — |  |  | (0.2 | ) |  | 2.0 |  |  | 14.0 |  |  | 61.3 |
Total | $ | 75.6 |  | $ | — |  | $ | (3.2 | ) | $ | 3.4 |  | $ | 13.1 |  | $ | 88.9 |
(a) The Revisions to Prior Estimates were primarily driven by changes in estimates associated with natural gas wells and compressor stations. We also have legally required AROs related to certain assets within our electric transmission and distribution systems. These retirement obligations are pursuant to an easement or franchise agreement and are only required if we discontinue our utility service under such easement or franchise agreement. Accordingly, it is not possible to estimate a time period when these obligations could be settled, and therefore, a liability for the cost of these obligations cannot be measured at this time.

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- Definition The entire disclosure for an asset retirement obligation and the associated long-lived asset. An asset retirement obligation is a legal obligation associated with the disposal or retirement from service of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 410 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147481850/410-20-50-1 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 410 -SubTopic 20 -Name Accounting Standards Codification -Publisher FASB -URI https://asc.fasb.org//410-20/tableOfContent Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name Accounting Standards Codification -Section 50 -Paragraph 2 -SubTopic 20 -Topic 410 -Publisher FASB -URI https://asc.fasb.org//1943274/2147481850/410-20-50-2 + Details
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