Quarterly financial information (unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 721.7	$ 683.3	$ 748.9	$ 666.8	$ 789.9	$ 739.2	$ 764.8	$ 721.2	$ 2,820.7	$ 3,015.1	$ 3,356.4
Gross profit	160.2	121.6	178.3	98.5	159.0	140.6	124.3	117.0	558.6	540.9
Income (loss) before income taxes	24.6	(15.2)	44.3	(33.2)	12.4	7.3	(50.8)	(27.7)	20.5	(58.8)	145.5
Net income (loss) attributable to Unisys Corporation common shareholders	$ (1.2)	$ (28.2)	$ 21.6	$ (39.9)	$ 1.1	$ (9.6)	$ (58.2)	$ (43.2)	$ (47.7)	$ (109.9)	$ 46.7
Earnings (loss) per common share attributable to Unisys Corporation
Basic (in dollars per share)	$ (0.02)	$ (0.56)	$ 0.43	$ (0.80)	$ 0.02	$ (0.19)	$ (1.17)	$ (0.87)	$ (0.95)	$ (2.20)	$ 0.89
Diluted (in dollars per share)	$ (0.02)	$ (0.56)	$ 0.36	$ (0.80)	$ 0.02	$ (0.19)	$ (1.17)	$ (0.87)	$ (0.95)	$ (2.20)	$ 0.89