Defined contribution and defined benefit retirement plans - Composition of Pension Plan Assets (Details) - Pension plans defined benefit - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Defined benefit pension plans [Line Items]
Plan assets	$ 480.6	$ 462.9
Quoted Prices in Active Markets (Level 1)
Defined benefit pension plans [Line Items]
Plan assets	138.6	111.7
Significant Other Observable Inputs (Level 2)
Defined benefit pension plans [Line Items]
Plan assets	17.4	19.5
Significant Unobservable Inputs (Level 3)
Defined benefit pension plans [Line Items]
Plan assets	286.0	292.1	$ 264.8
Assets measured at NAV
Defined benefit pension plans [Line Items]
Plan assets	38.6	39.6
Non U.S.
Defined benefit pension plans [Line Items]
Plan assets	$ 404.9	$ 422.6	$ 390.5
Long-term return on plan assets	4.90%	4.60%	2.50%
Germany
Defined benefit pension plans [Line Items]
Plan assets	$ 264.6	$ 269.4
Germany | Significant Unobservable Inputs (Level 3)
Defined benefit pension plans [Line Items]
Plan assets	264.6	269.4
Canada | Local Currency Equities
Defined benefit pension plans [Line Items]
Plan assets	2.8
Canada | Non Local Currency Equities
Defined benefit pension plans [Line Items]
Plan assets		2.7
Canada | Local Currency Fixed Income
Defined benefit pension plans [Line Items]
Plan assets	78.1	86.2
Canada | Cash and Other
Defined benefit pension plans [Line Items]
Plan assets	0.5	1.1
Canada | Quoted Prices in Active Markets (Level 1) | Local Currency Equities
Defined benefit pension plans [Line Items]
Plan assets	2.8
Canada | Quoted Prices in Active Markets (Level 1) | Non Local Currency Equities
Defined benefit pension plans [Line Items]
Plan assets		2.7
Canada | Quoted Prices in Active Markets (Level 1) | Local Currency Fixed Income
Defined benefit pension plans [Line Items]
Plan assets	78.1	86.2
Canada | Quoted Prices in Active Markets (Level 1) | Cash and Other
Defined benefit pension plans [Line Items]
Plan assets	0.5	1.1
Norway | Local Currency Equities
Defined benefit pension plans [Line Items]
Plan assets	2.0	2.4
Norway | Non Local Currency Equities
Defined benefit pension plans [Line Items]
Plan assets	6.9	7.2
Norway | Local Currency Fixed Income
Defined benefit pension plans [Line Items]
Plan assets	21.1	23.9
Norway | Cash and Other
Defined benefit pension plans [Line Items]
Plan assets	3.6	3.0
Norway | Non Local Currency Fixed Income
Defined benefit pension plans [Line Items]
Plan assets	4.2	4.2
Norway | Real Estate.
Defined benefit pension plans [Line Items]
Plan assets	$ 6.2	6.6
Long-term return on plan assets	7.00%
Norway | Fixed Income
Defined benefit pension plans [Line Items]
Long-term return on plan assets	5.00%
Norway | Quoted Prices in Active Markets (Level 1) | Local Currency Equities
Defined benefit pension plans [Line Items]
Plan assets	$ 2.0	2.4
Norway | Quoted Prices in Active Markets (Level 1) | Non Local Currency Equities
Defined benefit pension plans [Line Items]
Plan assets	6.9	7.2
Norway | Quoted Prices in Active Markets (Level 1) | Local Currency Fixed Income
Defined benefit pension plans [Line Items]
Plan assets	3.7	4.4
Norway | Quoted Prices in Active Markets (Level 1) | Cash and Other
Defined benefit pension plans [Line Items]
Plan assets	3.4	2.8
Norway | Quoted Prices in Active Markets (Level 1) | Non Local Currency Fixed Income
Defined benefit pension plans [Line Items]
Plan assets	4.2	4.2
Norway | Significant Other Observable Inputs (Level 2) | Local Currency Fixed Income
Defined benefit pension plans [Line Items]
Plan assets	$ 17.4	19.5
Norway | Significant Unobservable Inputs (Level 3)
Defined benefit pension plans [Line Items]
Percentage of plan asset allocation	15.00%
Norway | Significant Unobservable Inputs (Level 3) | Cash and Other
Defined benefit pension plans [Line Items]
Plan assets	$ 0.2	0.2
Norway | Significant Unobservable Inputs (Level 3) | Real Estate.
Defined benefit pension plans [Line Items]
Plan assets	6.2	6.6
Other.
Defined benefit pension plans [Line Items]
Plan assets	14.9	15.9
Other. | Significant Unobservable Inputs (Level 3)
Defined benefit pension plans [Line Items]
Plan assets	14.9	15.9
United States
Defined benefit pension plans [Line Items]
Plan assets	$ 75.7	$ 40.3	$ 39.1
Long-term return on plan assets	5.00%	5.00%	4.00%
United States | Cash and Other
Defined benefit pension plans [Line Items]
Plan assets	$ 38.2	$ 1.9
United States | Equities
Defined benefit pension plans [Line Items]
Plan assets	6.7	11.3
United States | Fixed Income
Defined benefit pension plans [Line Items]
Plan assets	30.8	27.1
United States | Quoted Prices in Active Markets (Level 1) | Cash and Other
Defined benefit pension plans [Line Items]
Plan assets	37.0	0.7
United States | Significant Unobservable Inputs (Level 3) | Equities
Defined benefit pension plans [Line Items]
Plan assets	0.1
United States | Assets measured at NAV | Cash and Other
Defined benefit pension plans [Line Items]
Plan assets	1.2	1.2
United States | Assets measured at NAV | Equities
Defined benefit pension plans [Line Items]
Plan assets	6.6	11.3
United States | Assets measured at NAV | Fixed Income
Defined benefit pension plans [Line Items]
Plan assets	$ 30.8	$ 27.1