Employee plans - Components of Net Periodic Benefit Expense (Details) - USD ($) $ in Millions		1 Months Ended			12 Months Ended
	Oct. 14, 2021	Nov. 30, 2023	Mar. 31, 2023	Jan. 31, 2021	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]					Other (expense), net
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Settlement losses					$ 348.9		$ 499.4
Pension Plans | U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost					0.0	$ 0.0	0.0
Interest cost					152.7	114.6	117.6
Expected return on plan assets					(178.6)	(189.8)	(199.8)
Amortization of prior service credit					(2.5)	(2.5)	(2.5)
Recognized net actuarial loss					75.6	125.9	135.6
Settlement losses	$ 130.1	$ 167.2	$ 181.0	$ 158.0	348.2	0.0	288.1
Net periodic pension expense (income)					395.4	48.2	339.0
Pension Plans | International Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost					1.1	1.9	3.0
Interest cost					72.3	39.3	36.7
Expected return on plan assets					(84.9)	(77.4)	(81.6)
Amortization of prior service credit					(2.4)	(2.6)	(2.8)
Recognized net actuarial loss					9.1	37.7	48.3
Settlement losses					0.7	0.0	211.3
Net periodic pension expense (income)					(4.1)	(1.1)	214.9
Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost					0.2	0.2	0.4
Interest cost					2.6	1.9	1.8
Expected return on plan assets					(0.3)	(0.3)	(0.3)
Amortization of prior service credit					(1.3)	(1.4)	(1.7)
Recognized net actuarial loss					(4.0)	(2.2)	(2.1)
Net periodic pension expense (income)					$ (2.8)	$ (1.8)	$ (1.9)