Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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Segment information - Summary of Operations by Segment (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenue	$ 744.8	$ 666.3	$ 666.2	$ 664.5	$ 721.7	$ 683.3	$ 748.9	$ 666.8	$ 2,741.8	$ 2,820.7	$ 3,015.1
Operating income (loss)									4.6	47.6	(55.1)
Depreciation and amortization									156.5	155.6	180.1
Total assets	2,542.4				2,021.6				2,542.4	2,021.6	2,130.0
Capital expenditures									176.5	147.1	213.7
Intersegment
Segment Reporting Information [Line Items]
Revenue									(25.9)	(22.6)	(49.0)
Operating Segments
Segment Reporting Information [Line Items]
Operating income (loss)									235.4	208.4	174.9
Total assets	1,364.5				1,339.0				1,364.5	1,339.0	1,486.0
Corporate
Segment Reporting Information [Line Items]
Revenue									(25.9)	(22.6)	(49.0)
Operating income (loss)									(230.8)	(160.8)	(230.0)
Total assets	1,177.9				682.6				1,177.9	682.6	644.0
Capital expenditures									4.3	3.0	1.9
Services
Segment Reporting Information [Line Items]
Revenue									2,328.2	2,406.3	2,605.6
Operating income (loss)									64.8	46.9	61.2
Depreciation and amortization									84.6	81.8	104.8
Total assets	985.9				963.3				985.9	963.3	1,081.7
Capital expenditures									102.7	74.8	143.3
Services \| Intersegment
Segment Reporting Information [Line Items]
Revenue									0.0	0.0	0.1
Services \| Operating Segments
Segment Reporting Information [Line Items]
Revenue									2,328.2	2,406.3	2,605.7
Technology
Segment Reporting Information [Line Items]
Revenue									413.6	414.4	409.5
Operating income (loss)									170.6	161.5	113.7
Depreciation and amortization									71.9	73.8	75.3
Total assets	$ 378.6				$ 375.7				378.6	375.7	404.3
Capital expenditures									69.5	69.3	68.5
Technology \| Intersegment
Segment Reporting Information [Line Items]
Revenue									25.9	22.6	48.9
Technology \| Operating Segments
Segment Reporting Information [Line Items]
Revenue									$ 439.5	$ 437.0	$ 458.4