CONSOLIDATED STATEMENTS OF DEFICIT (Unaudited) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ (263.8)	$ (285.8)	$ (312.1)	$ (238.7)	$ (209.4)	$ (1,228.3)	$ (312.1)	$ (1,228.3)
Consolidated net (loss) income	(18.5)	(142.3)	(157.5)	(12.9)	(78.6)	1,015.8	(318.3)	924.3
Capped call on conversion of notes			0.0
Stock-based activity	5.3	4.5	(1.3)	3.0	2.9	(0.5)
Translation adjustments	(36.5)	16.8	(17.1)	40.1	6.4	(87.6)	(36.8)	(41.1)
Postretirement plans	63.4	143.0	202.2	8.2	40.0	91.2	408.6	139.4
Ending balance	(250.1)	(263.8)	(285.8)	(200.3)	(238.7)	(209.4)	(250.1)	(200.3)
Total Unisys Corporation
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(308.8)	(331.6)	(356.8)	(274.3)	(244.7)	(1,265.4)	(356.8)	(1,265.4)
Consolidated net (loss) income	(18.7)	(140.8)	(157.8)	(12.9)	(78.6)	1,015.3
Stock-based activity	5.3	4.5	(1.3)	3.0	2.9	(0.5)
Translation adjustments	(33.9)	16.4	(17.9)	38.6	6.5	(81.6)
Postretirement plans	61.8	142.7	202.2	7.7	39.6	87.5
Ending balance	(294.3)	(308.8)	(331.6)	(237.9)	(274.3)	(244.7)	(294.3)	(237.9)
Common Stock Par Value
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	0.7	0.7	0.7	0.7	0.7	0.7	0.7	0.7
Ending balance	0.7	0.7	0.7	0.7	0.7	0.7	0.7	0.7
Accumulated Deficit
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(1,259.1)	(1,118.3)	(960.5)	(774.5)	(695.9)	(1,711.2)	(960.5)	(1,711.2)
Consolidated net (loss) income	(18.7)	(140.8)	(157.8)	(12.9)	(78.6)	1,015.3
Ending balance	(1,277.8)	(1,259.1)	(1,118.3)	(787.4)	(774.5)	(695.9)	(1,277.8)	(787.4)
Treasury Stock At Cost
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(152.1)	(151.9)	(114.4)	(114.3)	(114.2)	(109.6)	(114.4)	(109.6)
Capped call on conversion of notes			(30.8)
Stock-based activity		(0.2)	(6.7)	(0.1)	(0.1)	(4.6)
Ending balance	(152.1)	(152.1)	(151.9)	(114.4)	(114.3)	(114.2)	(152.1)	(114.4)
Paid-in Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	4,697.8	4,693.1	4,656.9	4,650.4	4,647.4	4,643.3	4,656.9	4,643.3
Capped call on conversion of notes			30.8
Stock-based activity	5.3	4.7	5.4	3.1	3.0	4.1
Ending balance	4,703.1	4,697.8	4,693.1	4,653.5	4,650.4	4,647.4	4,703.1	4,653.5
Accumulated Other Comprehensive Loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(3,596.1)	(3,755.2)	(3,939.5)	(4,036.6)	(4,082.7)	(4,088.6)	(3,939.5)	(4,088.6)
Translation adjustments	(33.9)	16.4	(17.9)	38.6	6.5	(81.6)
Postretirement plans	61.8	142.7	202.2	7.7	39.6	87.5
Ending balance	(3,568.2)	(3,596.1)	(3,755.2)	(3,990.3)	(4,036.6)	(4,082.7)	(3,568.2)	(3,990.3)
Non-controlling Interests
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	45.0	45.8	44.7	35.6	35.3	37.1	44.7	37.1
Consolidated net (loss) income	0.2	(1.5)	0.3			0.5
Translation adjustments	(2.6)	0.4	0.8	1.5	(0.1)	(6.0)
Postretirement plans	1.6	0.3	0.0	0.5	0.4	3.7
Ending balance	$ 44.2	$ 45.0	$ 45.8	$ 37.6	$ 35.6	$ 35.3	$ 44.2	$ 37.6