Share-based compensation - Fair Value Assumptions (Details) - LTIP linked to TRS - $ / shares	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Risk-free interest rate	4.25%	4.19%
Expected life in years	3 years	3 years
Expected volatility	52.50%	33.10%
Range of expected volatility for Peer Group, minimum rate	12.30%	28.70%
Range of expected volatility for Peer Group, maximum rate	52.50%	38.80%
Grant-date fair value (in dollars per share)	$ 17.28	$ 55.98