Earnings (Loss) Per Share - Computation of Earnings (Loss) Per Common Share Attributable to Unisys Corporation (Details) - USD ($) $ / shares in Units, shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Basic earnings (loss) per common share computation:
Net loss from continuing operations attributable to Unisys Corporation	$ (18,700,000)	$ (13,300,000)	$ (317,300,000)	$ (143,000,000.0)
Income from discontinued operations, net of tax	0	400,000	0	1,066,800,000
Net (loss) income attributable to Unisys Corporation	$ (18,700,000)	$ (12,900,000)	$ (317,300,000)	$ 923,800,000
Weighted average shares (in shares)	67,131	63,032	66,211	62,897
Basic earnings (loss) per share attributable to Unisys Corporation
Continuing operations (in dollars per share)	$ (0.28)	$ (0.21)	$ (4.79)	$ (2.27)
Discontinued operations (in dollars per share)	0	0.01	0	16.96
Total (in dollars per share)	$ (0.28)	$ (0.20)	$ (4.79)	$ 14.69
Diluted earnings (loss) per common share computation:
Net loss from continuing operations attributable to Unisys Corporation	$ (18,700,000)	$ (13,300,000)	$ (317,300,000)	$ (143,000,000.0)
Add interest expense on convertible senior notes, net of tax of zero	0	0	0	0
Interest expense on convertible senior notes, tax	0	0	0	0
Net loss from continuing operations attributable to Unisys Corporation for diluted earnings per share	(18,700,000)	(13,300,000)	(317,300,000)	(143,000,000.0)
Income from discontinued operations, net of tax	0	400,000	0	1,066,800,000
Net income (loss) attributable to Unisys Corporation for diluted earnings per share	$ (18,700,000)	$ (12,900,000)	$ (317,300,000)	$ 923,800,000
Weighted average shares (in shares)	67,131	63,032	66,211	62,897
Plus incremental shares from assumed conversions:
Employee stock plans (in shares)	0	0	0	0
Convertible senior notes (in shares)	0	0	0	0
Adjusted weighted average shares (in shares)	67,131	63,032	66,211	62,897
Diluted earnings (loss) per share attributable to Unisys Corporation
Continuing operations (in dollars per share)	$ (0.28)	$ (0.21)	$ (4.79)	$ (2.27)
Discontinued operations (in dollars per share)	0	0.01	0	16.96
Total (in dollars per share)	$ (0.28)	$ (0.20)	$ (4.79)	$ 14.69
Stock options and restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive weighted average securities (in shares)	764	998	857	892
Common shares issuable upon conversion of the convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive weighted average securities (in shares)	0	8,625	742	8,625