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Commitments and contingencies - Litigation (Details) - USD ($) $ in Millions | Sep. 30, 2025 | Dec. 31, 2024 | Sep. 30, 2024
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Commitments and Contingencies Disclosure [Abstract] |  |  |
Potential liabilities related to litigation and environmental matters | $ 25.1 | $ 24.1 | $ 22.0
Loss contingency, receivable | 1.9 | 0.0 | 0.0
Loss contingency, regulatory asset | $ 22.1 | $ 22.9 | $ 20.9

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- Definition Amount of loss contingency liability. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 450 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147483076/450-20-50-1 Reference 2: http://www.xbrl.org/2003/role/recommendedDisclosureRef -Topic 450 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 10 -Publisher FASB -URI https://asc.fasb.org/1943274/2147483076/450-20-50-10 + Details
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- Definition Amount of receivable related to a loss contingency accrual. For example, an insurance recovery receivable. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 460 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482425/460-10-50-3 + Details
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