Customer Funds - Gross Unrealized Losses and Related Fair Value of Investment (Detail) $ in Millions	Jun. 30, 2022 USD ($)
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Unrealized Losses	$ (76.6)
Less than 12 months, Fair Value	1,660.9
12 months or more, Unrealized Losses	(16.8)
12 months or more, Fair Value	189.8
Total, Unrealized Losses	(93.4)
Total, Fair Value	1,850.7
U.S. Government and Agencies Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Unrealized Losses	(26.9)
Less than 12 months, Fair Value	550.5
12 months or more, Unrealized Losses	(9.1)
12 months or more, Fair Value	112.2
Total, Unrealized Losses	(36.0)
Total, Fair Value	662.7
Canadian and Provincial Government Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Unrealized Losses	(15.6)
Less than 12 months, Fair Value	402.4
12 months or more, Unrealized Losses	(0.5)
12 months or more, Fair Value	6.3
Total, Unrealized Losses	(16.1)
Total, Fair Value	408.7
Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Unrealized Losses	(26.9)
Less than 12 months, Fair Value	508.7
12 months or more, Unrealized Losses	(5.2)
12 months or more, Fair Value	42.2
Total, Unrealized Losses	(32.1)
Total, Fair Value	550.9
Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Unrealized Losses	(4.7)
Less than 12 months, Fair Value	147.2
12 months or more, Unrealized Losses	(0.1)
12 months or more, Fair Value	5.4
Total, Unrealized Losses	(4.8)
Total, Fair Value	152.6
Mortgage-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Unrealized Losses	(0.1)
Less than 12 months, Fair Value	4.7
Total, Unrealized Losses	(0.1)
Total, Fair Value	4.7
Other Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Unrealized Losses	(2.4)
Less than 12 months, Fair Value	47.4
12 months or more, Unrealized Losses	(1.9)
12 months or more, Fair Value	23.7
Total, Unrealized Losses	(4.3)
Total, Fair Value	$ 71.1