Leases and commitments - Additional Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)
Lessee, Lease, Description [Line Items]
Optional extension or renewal term (up to)	5 years
Optional termination period	1 year
Standby letters of credit and surety bonds outstanding	$ 191
Deposits and collateralized assets	$ 8
Minimum
Lessee, Lease, Description [Line Items]
Initial lease terms	1 year
Maximum
Lessee, Lease, Description [Line Items]
Initial lease terms	8 years