Leases and commitments - Supplemental Balance Sheet Information (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Leases
Operating lease right-of-use assets	$ 79.3	$ 71.4	$ 0.0
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesCurrent	us-gaap:OtherLiabilitiesCurrent
Other accrued liabilities	$ 37.1	$ 34.1
Long-term operating lease liabilities	62.4	56.0
Total operating lease liabilities	$ 99.5	$ 90.1
Finance Leases
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	uis:OutsourcingAssetsNet	uis:OutsourcingAssetsNet
Outsourcing assets, net	$ 2.9	$ 4.6
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:LongTermDebtAndCapitalLeaseObligationsCurrent	us-gaap:LongTermDebtAndCapitalLeaseObligationsCurrent
Current maturities of long-term debt	$ 2.4	$ 1.8
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:LongTermDebtAndCapitalLeaseObligations	us-gaap:LongTermDebtAndCapitalLeaseObligations
Long-term debt	$ 3.1	$ 3.5
Total finance lease liabilities	$ 5.5	$ 5.3
Weighted-Average Remaining Lease Term (in years)
Operating leases	2 years 3 months 18 days	3 years 4 months 24 days
Finance leases	2 years	3 years
Weighted-Average Discount Rate
Operating leases	6.40%	6.40%
Finance leases	5.20%	5.00%