Recent Accounting Pronouncements Adoption of ASU 2017-07 - Restatement of Prior Year Amounts (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Costs of revenue		$ 1,857.9	$ 1,765.4	$ 1,644.5
General and administrative expenses		259.1	258.4	260.5
Sales and marketing expenses		168.2	169.5	169.8
Research and development expenses		98.4	93.5	80.5
Operating Income	[1]	397.3	319.3	276.6
Interest and non-operating expenses, net		$ 6.3	9.9	18.2
Reclass of Previously Reported General and Administrative Expenses			0.9
Accounting Standards Update 2017-07 [Member] | Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Costs of revenue			1,768.1	1,647.2
General and administrative expenses	[2]		264.9	275.0
Sales and marketing expenses			169.7	170.0
Research and development expenses			93.7	80.8
Operating Income			309.7	258.9
Interest and non-operating expenses, net			0.3	0.5
Accounting Standards Update 2017-07 [Member] | Restatement Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Costs of revenue			(2.7)	(2.7)
General and administrative expenses			(6.5)	(14.5)
Sales and marketing expenses			(0.2)	(0.2)
Research and development expenses			(0.2)	(0.3)
Operating Income			9.6	17.7
Interest and non-operating expenses, net			$ 9.6	$ 17.7

[1] (a)Operating income and operating margin for the years ended December 31, 2017 and 2016 has been restated to reflect the adoption of ASU 2017-07. Refer to Note 2, Recent Accounting Pronouncements for further information.

[2] (a)Previously reported General and administrative expenses of $0.9 have been reclassed to conform with current year presentation for the years ended December 31, 2017 and 2016, respectively, related to gains on the sale of long-lived assets.