Earnings (loss) per common share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Basic loss per common share computation:
Net loss attributable to Unisys Corporation	$ (430.7)	$ (106.0)	$ (448.5)
Weighted average shares (in shares)	68,254	67,665	66,451
Basic loss per common share (in dollars per share)	$ (6.31)	$ (1.57)	$ (6.75)
Diluted loss per common share computation:
Net loss attributable to Unisys Corporation	$ (430.7)	$ (106.0)	$ (448.5)
Weighted average shares (in shares)	68,254	67,665	66,451
Plus incremental shares from assumed conversions of employee stock plans (in shares)	0	0	0
Adjusted weighted average shares (in shares)	68,254	67,665	66,451
Diluted loss per common share (in dollars per share)	$ (6.31)	$ (1.57)	$ (6.75)
2021 Notes | Senior Notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stated interest rate (as a percentage)	5.50%
Restricted Stock Units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive weighted-average securities (in shares)	945	481	871
Common shares issuable upon conversion of the 5.50% convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive weighted-average securities (in shares)	0	0	557