Share-based compensation - Schedule of Long-Term Incentive Plan (LTIP) Linked to Total Return to Shareholders (Details) - LTIP linked to TRS - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Shares
Outstanding, beginning of period (in shares)	71,574	90,974	89,222
Granted (in shares)	27,123	26,469	46,024
Vested (issued or unissued and cancelled) (in shares)	(18,691)	(29,042)	(32,355)
Forfeited (in shares)	(3,529)	(16,827)	(11,917)
Outstanding, end of period (in shares)	76,477	71,574	90,974
Weighted-Average Grant-Date Fair Value Per Share
Outstanding, beginning of period (in dollars per share)	$ 47.67	$ 42.86	$ 42.10
Granted (in dollars per share)	55.98	54.92	41.12
Vested (issued or unissued and cancelled) (in dollars per share)	48.62	41.07	38.20
Forfeited (in dollars per share)	53.72	44.45	43.07
Outstanding, end of period (in dollars per share)	$ 50.11	$ 47.67	$ 42.86
Total weighted-average grant-date fair value of shares granted (in millions)	$ 1.5	$ 1.5	$ 1.9