Goodwill and Other Assets (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Line Items]
Goodwill	$ 1,422.5	$ 1,407.8	$ 1,289.0
Accumulated impairment losses	(290.7)	(290.7)	(290.7)
Beginning balance	1,117.1	998.3
Goodwill acquired		5.6
Goodwill adjustment		(2.9)
Currency translation adjustment	14.7	116.1
Ending balance	1,131.8	1,117.1
Services Segment [Member]
Goodwill [Line Items]
Goodwill	964.3	957.2	890.0
Accumulated impairment losses	(290.7)	(290.7)	(290.7)
Beginning balance	666.5	599.3
Goodwill acquired		5.6
Goodwill adjustment		(1.1)
Currency translation adjustment	7.1	62.7
Ending balance	673.6	666.5
Software Segment [Member]
Goodwill [Line Items]
Goodwill	258.3	254.0	224.9
Accumulated impairment losses	0.0	0.0	0.0
Beginning balance	254.0	224.9
Goodwill acquired		0.0
Goodwill adjustment		(1.0)
Currency translation adjustment	4.3	30.1
Ending balance	258.3	254.0
Systems Segment [Member]
Goodwill [Line Items]
Goodwill	199.9	196.6	174.1
Accumulated impairment losses	0.0	0.0	$ 0.0
Beginning balance	196.6	174.1
Goodwill acquired		0.0
Goodwill adjustment		(0.8)
Currency translation adjustment	3.3	23.3
Ending balance	$ 199.9	$ 196.6