Customer Funds - Investment of Customer Funds (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Money market securities, investments carried at cost and other cash equivalents, Fair Value	$ 1,562.4	$ 2,027.1
Invested customer funds, Fair Value	3,514.8	3,746.2
Receivables, Fair Value	21.0	13.2
Total customer funds, Fair Value	3,535.8	3,759.4
Money market securities, investments carried at cost and other cash equivalents, Amortized Cost	1,562.4	2,027.1
Invested customer funds, Amortized Cost	3,501.5	3,684.6
Receivables, Amortized Cost	18.4	13.2
Total customer funds, Amortized Cost	3,519.9	3,697.8
Amortized Cost	1,939.1	1,657.5
Gross Unrealized Gain	24.6	61.7
Gross Unrealized Loss	(11.3)	(0.1)
Fair value	1,952.4	1,719.1
U.S. Government and Agencies Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	697.8	494.0
Gross Unrealized Gain	9.5	21.6
Gross Unrealized Loss	(5.8)	(0.1)
Fair value	701.5	515.5
Canadian and Provincial Government Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	399.9	396.4
Gross Unrealized Gain	5.3	15.5
Gross Unrealized Loss	(1.3)
Fair value	403.9	411.9
Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	551.4	548.5
Gross Unrealized Gain	8.3	19.4
Gross Unrealized Loss	(3.1)
Fair value	556.6	567.9
Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	174.2	192.2
Gross Unrealized Gain	1.5	4.9
Gross Unrealized Loss	(0.3)
Fair value	175.4	197.1
Mortgage-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2.7	9.9
Gross Unrealized Gain		0.2
Fair value	2.7	10.1
Other Short-term Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	41.4
Fair value	41.4
Other Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	71.7	16.5
Gross Unrealized Gain		0.1
Gross Unrealized Loss	(0.8)
Fair value	$ 70.9	$ 16.6

Funds held for clients amortized cost.

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Invested customer funds amortized cost.

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Invested customer funds fair value.

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Money market securities investments carried at cost and other cash equivalents fair value.

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Receivables.

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Receivables amortized cost.

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Carrying amount as of the balance sheet date of the funds held on behalf of others and that are expected to be liquidated within one year or the normal operating cycle, if longer. This does not include funds held under reinsurance agreements.

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Investment in short-term money-market instruments (such as commercial paper, banker's acceptances, repurchase agreements, government securities, certificates of deposit, and so forth) which are highly liquid (that is, readily convertible to known amounts of cash) and so near their maturity that they present an insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify as cash equivalents by definition. Original maturity means an original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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