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Defined contribution and defined benefit retirement plans - Additional Information (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
	Dec. 16, 2025	Jun. 30, 2023	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Jul. 16, 2024
Defined benefit pension plans [Line Items]
Defined contribution plan expense			$ 8.4	$ 7.7	$ 8.2
Non cash defined benefit plan termination loss			28.7		6.2
Defined Benefit Pension Plans
Defined benefit pension plans [Line Items]
Non cash defined benefit plan termination loss		$ 6.2
Expected contribution			17.0
Expect to recognize unrecognized actuarial gains (losses)			0.1	1.7
Defined Benefit Pension Plans \| Louisiana Pigment Company
Defined benefit pension plans [Line Items]
Net pension asset						$ 10.6
Defined Benefit Pension Plans \| Non-U.S.
Defined benefit pension plans [Line Items]
Settlements			0.3	0.4	$ 6.5
Net overfunded status			$ (69.5)	$ (108.4)
Discount rate			4.30%	3.60%
Long-term return on plan assets			4.50%	4.90%	4.60%
Defined Benefit Pension Plans \| CANADA \| Equities \| Minimum
Defined benefit pension plans [Line Items]
Percentage of plan asset allocation			10.00%
Defined Benefit Pension Plans \| CANADA \| Fixed income \| Minimum
Defined benefit pension plans [Line Items]
Percentage of plan asset allocation			90.00%
Defined Benefit Pension Plans \| CANADA \| Fixed income \| Maximum
Defined benefit pension plans [Line Items]
Percentage of plan asset allocation			100.00%
Defined Benefit Pension Plans \| NORWAY \| Significant unobservable inputs (Level 3)
Defined benefit pension plans [Line Items]
Percentage of plan asset allocation			14.00%
Defined Benefit Pension Plans \| NORWAY \| Equities
Defined benefit pension plans [Line Items]
Long-term return on plan assets			8.00%
Percentage of plan asset allocation			18.00%
Defined Benefit Pension Plans \| NORWAY \| Fixed income
Defined benefit pension plans [Line Items]
Percentage of plan asset allocation			63.00%
Defined Benefit Pension Plans \| NORWAY \| Real Estate
Defined benefit pension plans [Line Items]
Long-term return on plan assets			7.00%
Percentage of plan asset allocation			14.00%
Defined Benefit Pension Plans \| NORWAY \| Other Investments And Liquid Funds
Defined benefit pension plans [Line Items]
Long-term return on plan assets			4.00%
Defined Benefit Pension Plans \| UNITED STATES
Defined benefit pension plans [Line Items]
Settlements	$ 28.7		$ 28.7
Net overfunded status	$ 9.0		$ 8.9	$ 10.5
Discount rate				5.50%
Long-term return on plan assets			5.00%	5.00%	5.00%
Percentage of remaining plan			10.00%