Summary of significant accounting policies - Additional Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) institution	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease to cost of revenue	$ (1,543.3)	$ (1,688.8)	$ (1,666.9)
Period of recognition in changes in fair value of plan assets	4 years
Technology
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease to cost of revenue	$ (113.9)	(98.2)	$ (99.1)
Intelligent Processing Solutions Ltd.
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Percentage of ownership interest	51.00%
Number of financial institutions that own remaining interests for which iPSL performs services | institution	3
Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease to cost of revenue		$ 19.8
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 | 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
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