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
	Mar. 31, 2021	Mar. 31, 2020
Basic earnings (loss) per common share computation:
Net loss from continuing operations attributable to Unisys Corporation	$ (157,800,000)	$ (53,200,000)
Income from discontinued operations, net of tax	0	1,068,500,000
Net income (loss) attributable to Unisys Corporation	$ (157,800,000)	$ 1,015,300,000
Weighted average shares (in shares)	64,423	62,650
Basic earnings (loss) per share attributable to Unisys Corporation
Continuing operations (in dollars per share)	$ (2.45)	$ (0.85)
Discontinued operations (in dollars per share)	0	17.06
Total (in dollars per share)	$ (2.45)	$ 16.21
Diluted earnings (loss) per common share computation:
Net loss from continuing operations attributable to Unisys Corporation	$ (157,800,000)	$ (53,200,000)
Add interest expense on convertible senior notes, net of tax of zero	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	(157,800,000)	(53,200,000)
Income from discontinued operations, net of tax	0	1,068,500,000
Net income (loss) attributable to Unisys Corporation for diluted earnings per share	$ (157,800,000)	$ 1,015,300,000
Weighted average shares (in shares)	64,423	62,650
Plus incremental shares from assumed conversions:
Employee stock plans (in shares)	0	0
Convertible senior notes (in shares)	0	0
Adjusted weighted average shares (in shares)	64,423	62,650
Diluted earnings (loss) per share attributable to Unisys Corporation
Continuing operations (in dollars per share)	$ (2.45)	$ (0.85)
Discontinued operations (in dollars per share)	0	17.06
Total (in dollars per share)	$ (2.45)	$ 16.21
Stock options and restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive weighted average securities (in shares)	1,067	875
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)	2,227	8,625
Convertible senior notes interest rate	5.50%