Earnings Per Share - Computation of Earnings (Loss) Per Common Share Attributable to Unisys Corporation (Details) - USD ($) $ / shares in Units, shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Basic earnings (loss) per common share computation:
Net loss from continuing operations attributable to Unisys Corporation	$ (140,800,000)	$ (76,500,000)	$ (298,600,000)	$ (129,700,000)
Income (loss) from discontinued operations, net of tax	0	(2,100,000)	0	1,066,400,000
Net income (loss) attributable to Unisys Corporation	$ (140,800,000)	$ (78,600,000)	$ (298,600,000)	$ 936,700,000
Weighted average shares (in shares)	67,080	63,010	65,752	62,830
Basic earnings (loss) per share attributable to Unisys Corporation
Continuing operations (in dollars per share)	$ (2.10)	$ (1.21)	$ (4.54)	$ (2.06)
Discontinued operations (in dollars per share)	0	(0.04)	0	16.97
Total (in dollars per share)	$ (2.10)	$ (1.25)	$ (4.54)	$ 14.91
Diluted earnings (loss) per common share computation:
Net loss from continuing operations attributable to Unisys Corporation	$ (140,800,000)	$ (76,500,000)	$ (298,600,000)	$ (129,700,000)
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
Net loss from continuing operations attributable to Unisys Corporation for diluted earnings per share	(140,800,000)	(76,500,000)	(298,600,000)	(129,700,000)
Income (loss) from discontinued operations, net of tax	0	(2,100,000)	0	1,066,400,000
Net income (loss) attributable to Unisys Corporation for diluted earnings per share	$ (140,800,000)	$ (78,600,000)	$ (298,600,000)	$ 936,700,000
Weighted average shares (in shares)	67,080	63,010	65,752	62,830
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)	67,080	63,010	65,752	62,830
Diluted earnings (loss) per share attributable to Unisys Corporation
Continuing operations (in dollars per share)	$ (2.10)	$ (1.21)	$ (4.54)	$ (2.06)
Discontinued operations (in dollars per share)	0	(0.04)	0	16.97
Total (in dollars per share)	$ (2.10)	$ (1.25)	$ (4.54)	$ 14.91
Stock options and restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive weighted average securities (in shares)	740	1,274	903	1,074
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	1,113	8,625