Earnings Per Share - Computation of Earnings (Loss) Per Common Share Attributable to Unisys Corporation (Detail) - USD ($) $ / shares in Units, shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Basic earnings (loss) per common share computation:
Net loss from continuing operations attributable to Unisys Corporation	$ (13,300,000)	$ (29,200,000)	$ (143,000,000.0)	$ (61,200,000)
Income from discontinued operations, net of tax	400,000	16,000,000.0	1,066,800,000	54,800,000
Net income (loss) attributable to Unisys Corporation	$ (12,900,000)	$ (13,200,000)	$ 923,800,000	$ (6,400,000)
Weighted average shares (in shares)	63,032	58,245	62,897	53,815
Basic earnings (loss) per share attributable to Unisys Corporation
Continuing operations (in dollars per share)	$ (0.21)	$ (0.50)	$ (2.27)	$ (1.14)
Discontinued operations (in dollars per share)	0.01	0.27	16.96	1.02
Total (in dollars per share)	$ (0.20)	$ (0.23)	$ 14.69	$ (0.12)
Diluted earnings (loss) per common share computation:
Net loss from continuing operations attributable to Unisys Corporation	$ (13,300,000)	$ (29,200,000)	$ (143,000,000.0)	$ (61,200,000)
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	0	0
Net loss from continuing operations attributable to Unisys Corporation for diluted earnings per share	(13,300,000)	(29,200,000)	(143,000,000.0)	(61,200,000)
Income from discontinued operations, net of tax	400,000	16,000,000.0	1,066,800,000	54,800,000
Net income (loss) attributable to Unisys Corporation for diluted earnings per share	$ (12,900,000)	$ (13,200,000)	$ 923,800,000	$ (6,400,000)
Weighted average shares (in shares)	63,032	58,245	62,897	53,815
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)	63,032	58,245	62,897	53,815
Diluted earnings (loss) per share attributable to Unisys Corporation
Continuing operations (in dollars per share)	$ (0.21)	$ (0.50)	$ (2.27)	$ (1.14)
Discontinued operations (in dollars per share)	0.01	0.27	16.96	1.02
Total (in dollars per share)	$ (0.20)	$ (0.23)	$ 14.69	$ (0.12)
Stock options and restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive weighted average securities (in shares)	998	1,462	892	1,394
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)	8,625	13,951	8,625	19,229
Convertible senior notes interest rate	5.50%		5.50%