Commitments and contingencies - Changes in Accrued Environmental Remediation and Related Costs (Details) $ in Millions	6 Months Ended
Jun. 30, 2026 USD ($) site	Dec. 31, 2025 USD ($)
Commitments and contingencies
Balance at the beginning of the period	$ 17.5
Additions charged to expense, net	1.0
Payments, net	(1.3)
Balance at the end of the period	17.2
Amounts recognized in the Condensed Consolidated Balance Sheet at the end of the period:
Current liabilities	2.7	$ 2.8
Noncurrent liabilities	14.5	14.7
Total	17.2	$ 17.5
Other Environmental Cleanup Matters
Commitments and contingencies
Balance at the end of the period	5.0
Amounts recognized in the Condensed Consolidated Balance Sheet at the end of the period:
Total	5.0
NLI \| Environmental Remediation Sites NL Named As PRP Or Defendant
Amounts recognized in the Condensed Consolidated Balance Sheet at the end of the period:
Aggregate income	$ 13.0
Number of sites associated with remediation and related costs \| site	27
Number of sites for which NL not currently able to reasonably estimate range of costs \| site	5
NLI \| Environmental Remediation Sites NL Named As PRP Or Defendant \| Maximum
Amounts recognized in the Condensed Consolidated Balance Sheet at the end of the period:
Upper end range, estimate costs for remediation and related matters	$ 38.0

Total costs accrued as of the balance sheet date for environmental loss contingencies.

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