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Summary of significant accounting policies - Additional Information (Details) $ / shares in Units, $ in Millions		3 Months Ended								6 Months Ended	12 Months Ended
	Sep. 27, 2019 USD ($) plan	Dec. 31, 2019 USD ($) institution $ / shares	Sep. 30, 2019 USD ($) $ / shares	Jun. 30, 2019 USD ($) $ / shares	Mar. 31, 2019 USD ($) $ / shares	Dec. 31, 2018 USD ($) $ / shares	Sep. 30, 2018 USD ($) $ / shares	Jun. 30, 2018 USD ($) $ / shares	Mar. 31, 2018 USD ($) $ / shares	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($) institution $ / shares	Dec. 31, 2018 USD ($) $ / shares	Dec. 31, 2017 USD ($) $ / shares
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease to cost of revenue											$ (2,282.3)	$ (2,138.7)	$ (2,194.1)
Increase to consolidated net income		$ (10.8)	$ (13.2)	$ 26.2	$ (19.4)	$ 25.0	$ 6.1	$ 3.8	$ 40.6		$ (17.2)	$ 75.5	$ (65.3)
Increase to diluted earnings per share (in dollars per share) \| $ / shares		$ (0.17)	$ (0.23)	$ 0.42	$ (0.38)	$ 0.41	$ 0.12	$ 0.07	$ 0.62		$ (0.31)	$ 1.30	$ (1.30)
Period of recognition in changes in fair value of plan assets											4 years
Advertising costs incurred											$ 3.6	$ 2.8	$ 1.6
Technology
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease to cost of revenue											$ (148.2)	$ (128.2)	$ (160.3)
Intelligent Processing Solutions Ltd.
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Percentage of ownership interest		51.00%									51.00%
Number of financial institutions that own remaining interests for which iPSL performs services \| institution		3									3
Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease to cost of revenue											$ 19.8
Increase to consolidated net income											$ 19.8
Increase to diluted earnings per share (in dollars per share) \| $ / shares											$ 0.35
Marketable Software
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Typical renewal period (on average)											5 years
Finite-lived intangible asset in process		$ 67.1									$ 67.1
Finite-lived intangible assets remaining		$ 119.7									$ 119.7
Weighted-average remaining life											3 years 2 months 12 days
Enterprise Software
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated revenue-producing lives of computer software products from the date of release											5 years
Enterprise software product as percentage of total marketable software											66.00%
Enterprise Software \| Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated revenue-producing lives of computer software products from the date of release											3 years
Remaining Products Classified as Marketable Software
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated revenue-producing lives of computer software products from the date of release											3 years
Minimum \| Technology
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Period over which payment is generally received for contracts											30 days
Maximum \| Technology
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Period over which payment is generally received for contracts											60 days
Buildings \| Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful lives											20 years
Buildings \| Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful lives											50 years
Machinery and office equipment \| Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful lives											4 years
Machinery and office equipment \| Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful lives											7 years
Rental equipment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful lives											4 years
Internal-use software \| Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful lives											3 years
Internal-use software \| Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful lives											10 years
Pension Plans
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Waiver to defer portion of required contributions to U.S. pension plans, number of plans \| plan	2
Defined Benefit Plan, Waiver to Defer Portion of Contributions, Potential Reduction of Required Cash Contribution if Granted	$ 115.0
U.S. Federal Business \| Discontinued Operation, Disposed of by Sale \| Subsequent Event \| Forecast
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash purchase price										$ 1,200.0