Employee benefit plans - Salaries and Employee Benefits Expense - Investment Percentages (Details) - Pension Benefits - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plan Disclosure
Amount of company's common stock included in equity securities	$ 0	$ 0
Equity Securities
Defined Benefit Plan Disclosure
Maximum diversification (as a percent)	10.00%
Maximum | Industry Sector
Defined Benefit Plan Disclosure
Maximum diversification (as a percent)	20.00%
Cash Equivalents
Defined Benefit Plan Disclosure
Defined benefit plan, target allocation (as a percent)	10.00%
Fixed Income
Defined Benefit Plan Disclosure
Defined benefit plan, target allocation (as a percent)	40.00%
Equity
Defined Benefit Plan Disclosure
Defined benefit plan, target allocation (as a percent)	50.00%