Employee plans - Funded Status of the Plan and Amounts Recognized in Consolidated Balance Sheet (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Amounts recognized in the consolidated balance sheets consist of:
Prepaid postretirement assets	$ 38.0	$ 119.5
Other accrued liabilities	(10.2)	(11.7)
Long-term postretirement liabilities	(787.7)	(714.6)
Pension Plans | U.S. Plans
Change in projected/accumulated benefit obligation
Benefit obligation at beginning of year	2,852.9	3,709.6
Service cost	0.0	0.0	$ 0.0
Interest cost	152.7	114.6	117.6
Plan participants’ contributions	0.0	0.0
Plan settlement	(516.1)	0.0
Actuarial (gain) loss	80.2	(668.1)
Benefits paid	(278.0)	(303.2)
Foreign currency translation adjustments	0.0	0.0
Benefit obligation at end of year	2,291.7	2,852.9	3,709.6
Change in plan assets
Fair value of plan assets at beginning of year	2,440.1	3,139.3
Actual return on plan assets	166.1	(401.9)
Employer contribution	5.8	5.9
Plan participants’ contributions	0.0	0.0
Plan settlement	(516.1)	0.0
Benefits paid	(278.0)	(303.2)
Foreign currency translation adjustments	0.0	0.0
Fair value of plan assets at end of year	1,817.9	2,440.1	3,139.3
Total funded status	(473.8)	(412.8)
Amounts recognized in the consolidated balance sheets consist of:
Prepaid postretirement assets	30.7	44.4
Other accrued liabilities	(5.4)	(5.4)
Long-term postretirement liabilities	(499.1)	(451.8)
Total funded status	(473.8)	(412.8)
Accumulated other comprehensive loss, net of tax
Net (income) loss	1,514.2	1,845.3
Prior service cost (credit)	(24.7)	(27.2)
Accumulated benefit obligation	2,291.7	2,852.9
Pension Plans | International Plans
Change in projected/accumulated benefit obligation
Benefit obligation at beginning of year	1,574.6	2,614.4
Service cost	1.1	1.9	3.0
Interest cost	72.3	39.3	36.7
Plan participants’ contributions	1.2	1.1
Plan settlement	(4.5)	0.0
Actuarial (gain) loss	67.7	(726.4)
Benefits paid	(80.9)	(86.4)
Foreign currency translation adjustments	83.9	(269.3)
Benefit obligation at end of year	1,715.4	1,574.6	2,614.4
Change in plan assets
Fair value of plan assets at beginning of year	1,444.3	2,431.6
Actual return on plan assets	18.7	(685.7)
Employer contribution	36.6	33.4
Plan participants’ contributions	1.2	1.1
Plan settlement	(4.5)	0.0
Benefits paid	(80.9)	(86.4)
Foreign currency translation adjustments	70.8	(249.7)
Fair value of plan assets at end of year	1,486.2	1,444.3	2,431.6
Total funded status	(229.2)	(130.3)
Amounts recognized in the consolidated balance sheets consist of:
Prepaid postretirement assets	7.3	75.1
Other accrued liabilities	(0.2)	(0.2)
Long-term postretirement liabilities	(236.3)	(205.2)
Total funded status	(229.2)	(130.3)
Accumulated other comprehensive loss, net of tax
Net (income) loss	1,037.8	859.7
Prior service cost (credit)	(45.0)	(44.9)
Accumulated benefit obligation	1,712.5	1,573.0
Other Postretirement Benefit Plans
Change in projected/accumulated benefit obligation
Benefit obligation at beginning of year	68.9	81.1
Service cost	0.2	0.2	0.4
Interest cost	2.6	1.9	1.8
Plan participants’ contributions	0.3	0.9
Actuarial (gain) loss	(6.9)	(16.1)
Benefits paid	(5.1)	(4.9)
Foreign currency translation adjustments	0.1	5.8
Benefit obligation at end of year	60.1	68.9	81.1
Change in plan assets
Fair value of plan assets at beginning of year	5.2	5.6
Actual return on plan assets	(2.8)	(0.7)
Employer contribution	5.6	4.3
Plan participants’ contributions	0.3	0.9
Benefits paid	(5.1)	(4.9)
Fair value of plan assets at end of year	3.2	5.2	$ 5.6
Total funded status	(56.9)	(63.7)
Amounts recognized in the consolidated balance sheets consist of:
Other accrued liabilities	(4.6)	(6.1)
Long-term postretirement liabilities	(52.3)	(57.6)
Total funded status	(56.9)	(63.7)
Accumulated other comprehensive loss, net of tax
Net (income) loss	(7.6)	(7.8)
Prior service cost (credit)	$ 0.6	$ (0.7)