Employee plans - Schedule of Plan Assets at Fair Value (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pension Plans | U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	$ 1,817.9	$ 2,440.1	$ 3,139.3
Pension Plans | U.S. Plans | Fair Value
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	1,382.2	1,945.9
Pension Plans | U.S. Plans | Fair Value | Common Stocks
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	361.5	544.6
Pension Plans | U.S. Plans | Fair Value | Equity Securities, Commingled Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	227.9	383.2
Pension Plans | U.S. Plans | Fair Value | U.S. Govt. Securities
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	289.8	291.7
Pension Plans | U.S. Plans | Fair Value | Other Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	245.1	293.8
Pension Plans | U.S. Plans | Fair Value | Debt Securities, Commingled Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	127.4	185.5
Pension Plans | U.S. Plans | Fair Value | Real Estate Investment Trusts
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	34.6	87.1
Pension Plans | U.S. Plans | Fair Value | Derivatives
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	89.9	95.0
Pension Plans | U.S. Plans | Fair Value | Pooled Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	80.0	92.1
Pension Plans | U.S. Plans | Fair Value | Cumulative futures contracts variation margin paid to (received from) brokers
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	(67.4)	5.3
Pension Plans | U.S. Plans | Fair Value | Cash
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	1.6	0.8
Pension Plans | U.S. Plans | Fair Value | Receivables
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	10.8	9.3
Pension Plans | U.S. Plans | Fair Value | Payables
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	(19.0)	(42.5)
Pension Plans | U.S. Plans | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	679.1	890.2
Pension Plans | U.S. Plans | Level 1 | Common Stocks
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	360.6	543.2
Pension Plans | U.S. Plans | Level 1 | U.S. Govt. Securities
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	289.8	291.7
Pension Plans | U.S. Plans | Level 1 | Real Estate Investment Trusts
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	34.6	87.1
Pension Plans | U.S. Plans | Level 1 | Derivatives
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	68.1	(4.7)
Pension Plans | U.S. Plans | Level 1 | Cumulative futures contracts variation margin paid to (received from) brokers
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	(67.4)	5.3
Pension Plans | U.S. Plans | Level 1 | Cash
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	1.6	0.8
Pension Plans | U.S. Plans | Level 1 | Receivables
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	10.8	9.3
Pension Plans | U.S. Plans | Level 1 | Payables
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	(19.0)	(42.5)
Pension Plans | U.S. Plans | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	703.1	1,055.7
Pension Plans | U.S. Plans | Level 2 | Common Stocks
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	0.9	1.4
Pension Plans | U.S. Plans | Level 2 | Equity Securities, Commingled Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	227.9	383.2
Pension Plans | U.S. Plans | Level 2 | Other Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	245.1	293.8
Pension Plans | U.S. Plans | Level 2 | Debt Securities, Commingled Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	127.4	185.5
Pension Plans | U.S. Plans | Level 2 | Derivatives
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	21.8	99.7
Pension Plans | U.S. Plans | Level 2 | Pooled Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	80.0	92.1
Pension Plans | U.S. Plans | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	0.0	0.0
Pension Plans | U.S. Plans | Level 3 | Common Stocks
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	0.0	0.0
Pension Plans | U.S. Plans | Plan assets measured using NAV as a practical expedient
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	435.7	494.2
Pension Plans | U.S. Plans | Plan assets measured using NAV as a practical expedient | Debt Securities, Commingled Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	102.3	65.0
Pension Plans | U.S. Plans | Plan assets measured using NAV as a practical expedient | Other, Commingled Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	96.8	147.4
Pension Plans | U.S. Plans | Plan assets measured using NAV as a practical expedient | Private Real Estate
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	188.9	238.9
Pension Plans | U.S. Plans | Plan assets measured using NAV as a practical expedient | Private Equity
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	47.7	42.9
Pension Plans | International Plans
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	1,486.2	1,444.3	2,431.6
Pension Plans | International Plans | Fair Value
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	946.7	411.1
Pension Plans | International Plans | Fair Value | Common Stocks
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	0.0	0.0
Pension Plans | International Plans | Fair Value | Other Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	360.3	2.8
Pension Plans | International Plans | Fair Value | Insurance Contracts
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	510.6	100.3
Pension Plans | International Plans | Fair Value | Debt Securities, Commingled Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	16.1	126.5
Pension Plans | International Plans | Fair Value | Derivatives
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	(3.4)
Pension Plans | International Plans | Fair Value | Other, Commingled Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	13.2	15.0
Pension Plans | International Plans | Fair Value | Pooled Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	12.0	25.3
Pension Plans | International Plans | Fair Value | Cash
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	37.9	20.5
Pension Plans | International Plans | Fair Value | Receivables
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	0.0	120.9
Pension Plans | International Plans | Fair Value | Payables
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	0.0	(0.2)
Pension Plans | International Plans | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	37.9	141.2
Pension Plans | International Plans | Level 1 | Common Stocks
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	0.0	0.0
Pension Plans | International Plans | Level 1 | Cash
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	37.9	20.5
Pension Plans | International Plans | Level 1 | Receivables
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	0.0	120.9
Pension Plans | International Plans | Level 1 | Payables
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	0.0	(0.2)
Pension Plans | International Plans | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	398.2	169.6
Pension Plans | International Plans | Level 2 | Common Stocks
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	0.0	0.0
Pension Plans | International Plans | Level 2 | Other Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	360.3	2.8
Pension Plans | International Plans | Level 2 | Debt Securities, Commingled Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	16.1	126.5
Pension Plans | International Plans | Level 2 | Derivatives
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	(3.4)
Pension Plans | International Plans | Level 2 | Other, Commingled Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	13.2	15.0
Pension Plans | International Plans | Level 2 | Pooled Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	12.0	25.3
Pension Plans | International Plans | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	510.6	100.3
Pension Plans | International Plans | Level 3 | Common Stocks
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	0.0	0.0
Pension Plans | International Plans | Level 3 | Insurance Contracts
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	510.6	100.3	110.2
Pension Plans | International Plans | Plan assets measured using NAV as a practical expedient
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	539.5	1,033.2
Pension Plans | International Plans | Plan assets measured using NAV as a practical expedient | Debt Securities, Commingled Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	191.4	788.8
Pension Plans | International Plans | Plan assets measured using NAV as a practical expedient | Other, Commingled Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	348.1	244.4
Pension Plans | International Plans | Plan assets measured using NAV as a practical expedient | Private Real Estate
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets
Pension Plans | International Plans | Plan assets measured using NAV as a practical expedient | Private Equity
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets
Other Postretirement Plans
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	3.2	5.2	5.6
Other Postretirement Plans | U.S. Plans | Insurance Contracts
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	3.2	5.2
Other Postretirement Plans | U.S. Plans | Level 3 | Insurance Contracts
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	$ 3.2	$ 5.2	$ 5.6