Customer Funds - Gross Unrealized Losses and Related Fair Value of Investment (Detail) $ in Millions	Mar. 31, 2022 USD ($)
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Unrealized Losses	$ (48.8)
Less than 12 months, Fair Value	1,122.6
12 months or more, Unrealized Losses	(11.6)
12 months or more, Fair Value	165.8
Total, Unrealized Losses	(60.4)
Total, Fair Value	1,288.4
U.S. Government and Agencies Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Unrealized Losses	(17.5)
Less than 12 months, Fair Value	368.1
12 months or more, Unrealized Losses	(7.8)
12 months or more, Fair Value	113.6
Total, Unrealized Losses	(25.3)
Total, Fair Value	481.7
Canadian and Provincial Government Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Unrealized Losses	(9.3)
Less than 12 months, Fair Value	243.0
12 months or more, Unrealized Losses	(0.4)
12 months or more, Fair Value	6.6
Total, Unrealized Losses	(9.7)
Total, Fair Value	249.6
Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Unrealized Losses	(17.1)
Less than 12 months, Fair Value	369.7
12 months or more, Unrealized Losses	(1.7)
12 months or more, Fair Value	23.0
Total, Unrealized Losses	(18.8)
Total, Fair Value	392.7
Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Unrealized Losses	(2.8)
Less than 12 months, Fair Value	98.1
Total, Unrealized Losses	(2.8)
Total, Fair Value	98.1
Other Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Unrealized Losses	(2.1)
Less than 12 months, Fair Value	43.7
12 months or more, Unrealized Losses	(1.7)
12 months or more, Fair Value	22.6
Total, Unrealized Losses	(3.8)
Total, Fair Value	$ 66.3