Customer Funds - Investment of Customer Funds (Detail) - USD ($) $ in Millions	Jun. 30, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Money market securities, investments carried at cost and other cash equivalents, Fair Value	$ 3,343.5	$ 1,562.4
Invested customer funds, Fair Value	5,385.8	3,514.8
Receivables, Fair Value	11.2	21.0
Total customer funds, Fair Value	5,397.0	3,535.8
Money market securities, investments carried at cost and other cash equivalents, Amortized Cost	3,343.5	1,562.4
Invested customer funds, Amortized Cost	5,478.5	3,501.5
Receivables, Amortized Cost	9.3	18.4
Total customer funds, Amortized Cost	5,487.8	3,519.9
Amortized Cost	2,135.0	1,939.1
Gross Unrealized Gain	0.7	24.6
Gross Unrealized Loss	(93.4)	(11.3)
Fair value	2,042.3	1,952.4
U.S. Government and Agencies Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	701.1	697.8
Gross Unrealized Gain		9.5
Gross Unrealized Loss	(36.0)	(5.8)
Fair value	665.1	701.5
Canadian and Provincial Government Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	454.6	399.9
Gross Unrealized Gain	0.2	5.3
Gross Unrealized Loss	(16.1)	(1.3)
Fair value	438.7	403.9
Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	649.1	551.4
Gross Unrealized Gain	0.5	8.3
Gross Unrealized Loss	(32.1)	(3.1)
Fair value	617.5	556.6
Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	180.1	174.2
Gross Unrealized Gain		1.5
Gross Unrealized Loss	(4.8)	(0.3)
Fair value	175.3	175.4
Mortgage-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5.0	2.7
Gross Unrealized Loss	(0.1)
Fair value	4.9	2.7
Other Short-Term Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	69.6	41.4
Fair value	69.6	41.4
Other Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	75.5	71.7
Gross Unrealized Loss	(4.3)	(0.8)
Fair value	$ 71.2	$ 70.9

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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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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