Commitments and contingencies - Schedule of Contractual Obligations (Details) $ in Millions	Sep. 30, 2024 USD ($)
Other Commitments [Line Items]
Total	$ 965.1
Less than 1 year	143.1
1 - 3 years	180.4
3 - 5 years	482.3
More than 5 years	159.3
Accounts payable and accrued liabilities
Other Commitments [Line Items]
Total	132.6
Less than 1 year	129.3
1 - 3 years	3.3
3 - 5 years	0.0
More than 5 years	0.0
Lease liabilities
Other Commitments [Line Items]
Total	221.8
Less than 1 year	13.6
1 - 3 years	13.4
3 - 5 years	36.6
More than 5 years	158.2
Restoration provisions
Other Commitments [Line Items]
Total	1.6
Less than 1 year	0.2
1 - 3 years	0.0
3 - 5 years	0.3
More than 5 years	1.1
Convertible debt principal
Other Commitments [Line Items]
Total	375.0
Less than 1 year	0.0
1 - 3 years	100.0
3 - 5 years	275.0
More than 5 years	0.0
Convertible debt interest
Other Commitments [Line Items]
Total	234.1
Less than 1 year	0.0
1 - 3 years	63.7
3 - 5 years	170.4
More than 5 years	$ 0.0