Retirement plans - Narrative (Details) - USD ($)	6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022
TRP
Defined Benefit Plan Disclosure [Line Items]
Total net pension obligations	$ 79,000,000
Cash contributions	0	$ 0
TRP | Accrued Liabilities
Defined Benefit Plan Disclosure [Line Items]
Total net pension obligations	5,600,000
SERP
Defined Benefit Plan Disclosure [Line Items]
Cash contributions	1,900,000	$ 1,900,000
Additional cash payments	$ 3,000,000