Consolidated Statements of Deficit (Unaudited) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ (238.7)	$ (209.4)	$ (1,228.3)	$ (1,213.7)	$ (1,282.5)	$ (1,299.6)	$ (1,228.3)	$ (1,299.6)
Consolidated net income (loss)	(12.9)	(78.6)	1,015.8	(9.4)	29.8	(16.8)	924.3	3.6
Stock-based activity	3.0	2.9	(0.5)	2.9	2.4	(0.4)
Debt exchange				83.9
Capped call on debt exchange				7.2
Translation adjustments	40.1	6.4	(87.6)	(51.7)	(13.8)	(34.2)	(41.1)	(99.7)
Postretirement plans	8.2	40.0	91.2	63.4	50.4	68.5	139.4	182.3
Ending balance	(200.3)	(238.7)	(209.4)	(1,117.4)	(1,213.7)	(1,282.5)	(200.3)	(1,117.4)
Total Unisys Corporation
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(274.3)	(244.7)	(1,265.4)	(1,260.8)	(1,326.9)	(1,343.5)	(1,265.4)	(1,343.5)
Consolidated net income (loss)	(12.9)	(78.6)	1,015.3	(13.2)	26.2	(19.4)
Stock-based activity	3.0	2.9	(0.5)	2.9	2.4	(0.4)
Debt exchange				83.9
Capped call on debt exchange				7.2
Translation adjustments	38.6	6.5	(81.6)	(49.0)	(11.6)	(32.8)
Postretirement plans	7.7	39.6	87.5	61.9	49.1	69.2
Ending balance	(237.9)	(274.3)	(244.7)	(1,167.1)	(1,260.8)	(1,326.9)	(237.9)	(1,167.1)
Common Stock Par Value
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	0.7	0.7	0.7	0.6	0.6	0.5	0.7	0.5
Stock-based activity						0.1
Debt exchange				0.1
Ending balance	0.7	0.7	0.7	0.7	0.6	0.6	0.7	0.7
Accumulated Deficit
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(774.5)	(695.9)	(1,711.2)	(1,687.2)	(1,713.4)	(1,694.0)	(1,711.2)	(1,694.0)
Consolidated net income (loss)	(12.9)	(78.6)	1,015.3	(13.2)	26.2	(19.4)
Ending balance	(787.4)	(774.5)	(695.9)	(1,700.4)	(1,687.2)	(1,713.4)	(787.4)	(1,700.4)
Treasury Stock At Cost
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(114.3)	(114.2)	(109.6)	(109.5)	(109.4)	(105.0)	(109.6)	(105.0)
Stock-based activity	(0.1)	(0.1)	(4.6)	(0.1)	(0.1)	(4.4)
Ending balance	(114.4)	(114.3)	(114.2)	(109.6)	(109.5)	(109.4)	(114.4)	(109.6)
Paid-in Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	4,650.4	4,647.4	4,643.3	4,546.2	4,543.7	4,539.8	4,643.3	4,539.8
Stock-based activity	3.1	3.0	4.1	3.0	2.5	3.9
Debt exchange				83.8
Capped call on debt exchange				7.2
Ending balance	4,653.5	4,650.4	4,647.4	4,640.2	4,546.2	4,543.7	4,653.5	4,640.2
Accumulated Other Comprehensive Loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(4,036.6)	(4,082.7)	(4,088.6)	(4,010.9)	(4,048.4)	(4,084.8)	(4,088.6)	(4,084.8)
Translation adjustments	38.6	6.5	(81.6)	(49.0)	(11.6)	(32.8)
Postretirement plans	7.7	39.6	87.5	61.9	49.1	69.2
Ending balance	(3,990.3)	(4,036.6)	(4,082.7)	(3,998.0)	(4,010.9)	(4,048.4)	(3,990.3)	(3,998.0)
Noncontrolling Interests
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	35.6	35.3	37.1	47.1	44.4	43.9	37.1	43.9
Consolidated net income (loss)			0.5	3.8	3.6	2.6
Translation adjustments	1.5	(0.1)	(6.0)	(2.7)	(2.2)	(1.4)
Postretirement plans	0.5	0.4	3.7	1.5	1.3	(0.7)
Ending balance	$ 37.6	$ 35.6	$ 35.3	$ 49.7	$ 47.1	$ 44.4	$ 37.6	$ 49.7