Consolidated Statements of Deficit (Unaudited) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Jan. 01, 2018
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ (1,213.7)	$ (1,282.5)	$ (1,299.6)	$ (1,244.1)	$ (1,270.8)	$ (1,326.5)	$ (1,299.6)	$ (1,326.5)
Cumulative effect adjustment - ASU No. 2014-09									$ (21.4)
Reclassification pursuant to ASU No. 2018-02				0.0
Consolidated net income (loss)	(9.4)	29.8	(16.8)	7.0	6.0	41.7	3.6	54.7
Stock-based activity	2.9	2.4	(0.4)	2.4	4.1	1.5
Debt exchange	83.9
Capped call on debt exchange	7.2
Translation adjustments	(51.7)	(13.8)	(34.2)	(8.2)	(23.3)	(5.1)	(99.7)	(36.6)
Postretirement plans	63.4	50.4	68.5	39.1	39.9	39.0	182.3	118.0
Ending balance	(1,117.4)	(1,213.7)	(1,282.5)	(1,203.8)	(1,244.1)	(1,270.8)	(1,117.4)	(1,203.8)
Total Unisys Corporation
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(1,260.8)	(1,326.9)	(1,343.5)	(1,275.5)	(1,301.3)	(1,354.7)	(1,343.5)	(1,354.7)
Cumulative effect adjustment - ASU No. 2014-09									(21.4)
Reclassification pursuant to ASU No. 2018-02				0.0
Consolidated net income (loss)	(13.2)	26.2	(19.4)	6.1	3.8	40.6
Stock-based activity	2.9	2.4	(0.4)	2.4	4.1	1.5
Debt exchange	83.9
Capped call on debt exchange	7.2
Translation adjustments	(49.0)	(11.6)	(32.8)	(7.8)	(21.6)	(5.9)
Postretirement plans	61.9	49.1	69.2	38.8	39.5	38.6
Ending balance	(1,167.1)	(1,260.8)	(1,326.9)	(1,236.0)	(1,275.5)	(1,301.3)	(1,167.1)	(1,236.0)
Common Stock Par Value
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	0.6	0.6	0.5	0.5	0.5	0.5	0.5	0.5
Stock-based activity			0.1
Debt exchange	0.1
Ending balance	0.7	0.6	0.6	0.5	0.5	0.5	0.7	0.5
Accumulated Deficit
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(1,687.2)	(1,713.4)	(1,694.0)	(1,940.1)	(1,943.9)	(1,963.1)	(1,694.0)	(1,963.1)
Cumulative effect adjustment - ASU No. 2014-09									$ (21.4)
Reclassification pursuant to ASU No. 2018-02				208.7
Consolidated net income (loss)	(13.2)	26.2	(19.4)	6.1	3.8	40.6
Ending balance	(1,700.4)	(1,687.2)	(1,713.4)	(1,725.3)	(1,940.1)	(1,943.9)	(1,700.4)	(1,725.3)
Treasury Stock At Cost
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(109.5)	(109.4)	(105.0)	(104.8)	(104.8)	(102.7)	(105.0)	(102.7)
Stock-based activity	(0.1)	(0.1)	(4.4)	(0.1)		(2.1)
Ending balance	(109.6)	(109.5)	(109.4)	(104.9)	(104.8)	(104.8)	(109.6)	(104.9)
Paid-in Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	4,546.2	4,543.7	4,539.8	4,534.1	4,530.0	4,526.4	4,539.8	4,526.4
Stock-based activity	3.0	2.5	3.9	2.5	4.1	3.6
Debt exchange	83.8
Capped call on debt exchange	7.2
Ending balance	4,640.2	4,546.2	4,543.7	4,536.6	4,534.1	4,530.0	4,640.2	4,536.6
Accumulated Other Comprehensive Loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(4,010.9)	(4,048.4)	(4,084.8)	(3,765.2)	(3,783.1)	(3,815.8)	(4,084.8)	(3,815.8)
Reclassification pursuant to ASU No. 2018-02				(208.7)
Translation adjustments	(49.0)	(11.6)	(32.8)	(7.8)	(21.6)	(5.9)
Postretirement plans	61.9	49.1	69.2	38.8	39.5	38.6
Ending balance	(3,998.0)	(4,010.9)	(4,048.4)	(3,942.9)	(3,765.2)	(3,783.1)	(3,998.0)	(3,942.9)
Noncontrolling Interests
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	47.1	44.4	43.9	31.4	30.5	28.2	43.9	28.2
Consolidated net income (loss)	3.8	3.6	2.6	0.9	2.2	1.1
Translation adjustments	(2.7)	(2.2)	(1.4)	(0.4)	(1.7)	0.8
Postretirement plans	1.5	1.3	(0.7)	0.3	0.4	0.4
Ending balance	$ 49.7	$ 47.1	$ 44.4	$ 32.2	$ 31.4	$ 30.5	$ 49.7	$ 32.2