Employee plans - Schedule of Plan Assets at Fair Value (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Pension Plans | U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	$ 3,139.3	$ 3,847.8	$ 3,334.2
Pension Plans | U.S. Plans | Fair Value
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	2,688.7	3,403.4
Pension Plans | U.S. Plans | Fair Value | Common Stocks
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	654.3	774.1
Pension Plans | U.S. Plans | Fair Value | Equity Securities, Commingled Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	398.9	640.6
Pension Plans | U.S. Plans | Fair Value | U.S. Govt. Securities
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	413.2	388.5
Pension Plans | U.S. Plans | Fair Value | Other Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	479.3	589.9
Pension Plans | U.S. Plans | Fair Value | Debt Securities, Commingled Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	525.2	689.9
Pension Plans | U.S. Plans | Fair Value | Real Estate Investment Trusts
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	154.1	112.1
Pension Plans | U.S. Plans | Fair Value | Derivatives
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	(53.7)	(67.3)
Pension Plans | U.S. Plans | Fair Value | Pooled Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	108.4	233.4
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	(5.8)	(1.1)
Pension Plans | U.S. Plans | Fair Value | Cash
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	0.2	21.8
Pension Plans | U.S. Plans | Fair Value | Receivables
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	15.7	28.8
Pension Plans | U.S. Plans | Fair Value | Payables
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	(1.1)	(7.3)
Pension Plans | U.S. Plans | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	1,234.5	1,319.0
Pension Plans | U.S. Plans | Level 1 | Common Stocks
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	652.4	771.2
Pension Plans | U.S. Plans | Level 1 | U.S. Govt. Securities
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	413.2	388.5
Pension Plans | U.S. Plans | Level 1 | Real Estate Investment Trusts
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	154.1	112.1
Pension Plans | U.S. Plans | Level 1 | Derivatives
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	5.8	5.0
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	(5.8)	(1.1)
Pension Plans | U.S. Plans | Level 1 | Cash
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	0.2	21.8
Pension Plans | U.S. Plans | Level 1 | Receivables
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	15.7	28.8
Pension Plans | U.S. Plans | Level 1 | Payables
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	(1.1)	(7.3)
Pension Plans | U.S. Plans | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	1,454.2	2,084.4
Pension Plans | U.S. Plans | Level 2 | Common Stocks
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	1.9	2.9
Pension Plans | U.S. Plans | Level 2 | Equity Securities, Commingled Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	398.9	640.6
Pension Plans | U.S. Plans | Level 2 | Other Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	479.3	589.9
Pension Plans | U.S. Plans | Level 2 | Debt Securities, Commingled Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	525.2	689.9
Pension Plans | U.S. Plans | Level 2 | Derivatives
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	(59.5)	(72.3)
Pension Plans | U.S. Plans | Level 2 | Pooled Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	108.4	233.4
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	450.6	444.4
Pension Plans | U.S. Plans | Plan assets measured using NAV as a practical expedient | Equity Securities, Commingled Funds
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 | Debt Securities, Commingled Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	78.6	121.7
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	112.5	104.2
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	234.2	208.0
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	25.3	10.5
Pension Plans | International Plans
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	2,431.6	3,129.4	2,816.4
Pension Plans | International Plans | Fair Value
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	949.8	1,552.9
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 | Equity Securities, Commingled Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	34.1	153.4
Pension Plans | International Plans | Fair Value | Other Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	3.0	125.8
Pension Plans | International Plans | Fair Value | Insurance Contracts
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	110.2	127.5
Pension Plans | International Plans | Fair Value | Debt Securities, Commingled Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	383.8	471.2
Pension Plans | International Plans | Fair Value | Real Estate Investment Trusts
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		2.0
Pension Plans | International Plans | Fair Value | Derivatives
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		20.5
Pension Plans | International Plans | Fair Value | Other, Commingled Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	390.0	381.4
Pension Plans | International Plans | Fair Value | Pooled Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		178.0
Pension Plans | International Plans | Fair Value | Cash
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	28.7	111.7
Pension Plans | International Plans | Fair Value | Receivables
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		2.1
Pension Plans | International Plans | Fair Value | Payables
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		(20.7)
Pension Plans | International Plans | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	28.7	93.1
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	28.7	111.7
Pension Plans | International Plans | Level 1 | Receivables
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		2.1
Pension Plans | International Plans | Level 1 | Payables
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		(20.7)
Pension Plans | International Plans | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	810.9	1,332.3
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 | Equity Securities, Commingled Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	34.1	153.4
Pension Plans | International Plans | Level 2 | Other Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	3.0	125.8
Pension Plans | International Plans | Level 2 | Debt Securities, Commingled Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	383.8	471.2
Pension Plans | International Plans | Level 2 | Real Estate Investment Trusts
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		2.0
Pension Plans | International Plans | Level 2 | Derivatives
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		20.5
Pension Plans | International Plans | Level 2 | Other, Commingled Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	390.0	381.4
Pension Plans | International Plans | Level 2 | Pooled Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		178.0
Pension Plans | International Plans | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	110.2	127.5
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	110.2	127.5	123.1
Pension Plans | International Plans | Plan assets measured using NAV as a practical expedient
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	1,481.8	1,576.5
Pension Plans | International Plans | Plan assets measured using NAV as a practical expedient | Equity Securities, Commingled Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	404.5	429.9
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	1,077.3	1,067.4
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	0.0	27.4
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	0.0	51.8
Other Postretirement Plans
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	5.6	6.0	6.9
Other Postretirement Plans | U.S. Plans | Insurance Contracts
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	5.6	6.0
Other Postretirement Plans | U.S. Plans | Level 3 | Insurance Contracts
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	$ 5.6	$ 6.0	$ 6.9