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Asset Retirement Obligations (Tables) | 12 Months Ended
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Dec. 31, 2023
Asset Retirement Obligation Disclosure [Abstract] |
Schedule of changes to asset retirement obligations | The following table shows changes to our AROs during the years ended December 31:
(in millions) |  | 2023 |  | 2022 |  | 2021
Balance as of January 1 |  | $ | 479.3 |  |  | $ | 462.0 |  |  | $ | 513.5 |  |
Accretion |  | 17.2 |  |  | 16.1 |  |  | 21.2 |  |
Additions |  | 24.0 |  | (1) | 12.8 |  | (3) | 31.0 |  | (4)
Revisions to estimated cash flows |  | (133.5) |  | (2) | 2.2 |  |  | (84.9) |  | (5)
Liabilities settled |  | (12.8) |  |  | (13.8) |  |  | (18.8) |  |
Balance as of December 31 |  | $ | 374.2 |  |  | $ | 479.3 |  |  | $ | 462.0 |  |
(1) AROs increased primarily as a result of AROs being recorded for the legal requirement to dismantle, at retirement, the Red Barn wind-powered generation project, the Badger Hollow II solar generation project, and the Sapphire Sky and Samson I non-utility renewable generation projects. (2) AROs decreased primarily due to revisions made to estimated cash flows for changes in removal cost estimates and settlements dates for mains and services at PGL and NSG. (3) AROs increased primarily as a result of an ARO being recorded for the legal requirement to dismantle, at retirement, the Thunderhead non-utility wind generation project. (4) AROs increased as a result of AROs being recorded for the legal requirement to dismantle, at retirement, the Badger Hollow I solar generation project and the Tatanka Ridge and Jayhawk non-utility renewable generation projects. (5) AROs decreased due to revisions made to estimated cash flows primarily for changes in the cost to retire natural gas distribution lines at PGL and NSG. Partially offsetting this decrease were revisions made to removal estimates for wind generation projects at WE and WPS and for fly ash landfills and ash ponds at WPS.

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- Definition Tabular disclosure of the changes in carrying amount of a liability for asset retirement obligations, for changes such as new obligations, changes in estimates of existing obligations, spending on existing obligations, property dispositions, and foreign currency translation. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 410 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org//1943274/2147481850/410-20-50-1 + Details
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