Fair value measurements - Significant unobservable inputs used for recurring fair value measurements (Details) $ in Millions	Dec. 31, 2021 USD ($) $ / shares	Feb. 26, 2021 USD ($)	Dec. 31, 2020 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other long-term investments	$ 456.1		$ 4.0
Liability-classified capital instruments	(87.8)	$ (137.6)	0.0
Private equity funds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other long-term investments	125.4
Series A preference shares
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Liability-classified capital instruments	(20.4)	$ (40.8)
Significant unobservable inputs (Level 3)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other long-term investments	336.9		$ 4.0
Liability-classified capital instruments	(57.2)
Significant unobservable inputs (Level 3) | Fair Value, Recurring | Third party appraisal
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative instruments	$ (3.8)
Significant unobservable inputs (Level 3) | Fair Value, Recurring | Third party appraisal | Broker quotes
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative instruments, Unobservable input	(3.8)
Significant unobservable inputs (Level 3) | Fair Value, Recurring | Private equity securities | Market multiple analysis
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other long-term investments	$ 156.1
Significant unobservable inputs (Level 3) | Fair Value, Recurring | Private equity securities | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other long-term investments	$ 40.0
Significant unobservable inputs (Level 3) | Fair Value, Recurring | Private equity securities | Discounted cash flow | Share price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other long-term investments, Unobservable input | $ / shares	51.26
Significant unobservable inputs (Level 3) | Fair Value, Recurring | Private equity funds | Net asset value discount
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other long-term investments	$ 80.6
Significant unobservable inputs (Level 3) | Fair Value, Recurring | Private equity funds | Net asset value discount | Discount | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other long-term investments, Unobservable input	0.05
Significant unobservable inputs (Level 3) | Fair Value, Recurring | Private equity funds | Net asset value discount | Discount | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other long-term investments, Unobservable input	0.50
Significant unobservable inputs (Level 3) | Fair Value, Recurring | Private debt instrument | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other long-term investments	$ 5.7
Significant unobservable inputs (Level 3) | Fair Value, Recurring | Private debt instrument | Discounted cash flow | Discount | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other long-term investments, Unobservable input	0.0474
Significant unobservable inputs (Level 3) | Fair Value, Recurring | Private debt instrument | Discounted cash flow | Discount | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other long-term investments, Unobservable input	0.0570
Significant unobservable inputs (Level 3) | Fair Value, Recurring | Private debt instrument | Discounted cash flow | Discount | Median
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other long-term investments, Unobservable input	0.0514
Significant unobservable inputs (Level 3) | Fair Value, Recurring | Series A preference shares | Model simulation
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Liability-classified capital instruments	$ (20.4)
Significant unobservable inputs (Level 3) | Fair Value, Recurring | Series A preference shares | Model simulation | Share price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Liability-classified capital instruments measurement input | $ / shares	1.74
Significant unobservable inputs (Level 3) | Fair Value, Recurring | Warrants | Pricing model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Liability-classified capital instruments	$ (36.8)