Income taxes - Net operating loss and capital loss carryforwards (Details) $ in Millions	Dec. 31, 2021 USD ($)
Operating Loss Carryforwards [Line Items]
No expiration date	$ 1,110.6
Total	1,266.4
Gross deferred tax asset	292.6
Valuation allowance	(99.1)
Net deferred tax asset	193.5
2022-2026
Operating Loss Carryforwards [Line Items]
Subject to expiration	4.7
2027-2041
Operating Loss Carryforwards [Line Items]
Subject to expiration	151.1
U.S. | Foreign
Operating Loss Carryforwards [Line Items]
No expiration date	21.1
Total	133.6
Gross deferred tax asset	19.4
Valuation allowance	0.0
Net deferred tax asset	19.4
U.S. | 2022-2026 | Foreign
Operating Loss Carryforwards [Line Items]
Subject to expiration	4.7
U.S. | 2027-2041 | Foreign
Operating Loss Carryforwards [Line Items]
Subject to expiration	107.8
Luxembourg | Foreign
Operating Loss Carryforwards [Line Items]
No expiration date	724.1
Total	767.4
Gross deferred tax asset	191.4
Valuation allowance	(62.1)
Net deferred tax asset	129.3
Luxembourg | 2022-2026 | Foreign
Operating Loss Carryforwards [Line Items]
Subject to expiration	0.0
Luxembourg | 2027-2041 | Foreign
Operating Loss Carryforwards [Line Items]
Subject to expiration	43.3
Sweden | Foreign
Operating Loss Carryforwards [Line Items]
No expiration date	217.4
Total	217.4
Gross deferred tax asset	44.8
Valuation allowance	0.0
Net deferred tax asset	44.8
Sweden | 2022-2026 | Foreign
Operating Loss Carryforwards [Line Items]
Subject to expiration	0.0
Sweden | 2027-2041 | Foreign
Operating Loss Carryforwards [Line Items]
Subject to expiration	0.0
U.K. | Foreign
Operating Loss Carryforwards [Line Items]
No expiration date	148.0
Total	148.0
Gross deferred tax asset	37.0
Valuation allowance	(37.0)
Net deferred tax asset	0.0
U.K. | 2022-2026 | Foreign
Operating Loss Carryforwards [Line Items]
Subject to expiration	0.0
U.K. | 2027-2041 | Foreign
Operating Loss Carryforwards [Line Items]
Subject to expiration	$ 0.0