Customer Funds - Gross Unrealized Losses and Related Fair Value of Investment (Detail) $ in Millions	Mar. 31, 2021 USD ($)
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Unrealized Losses	$ (2.9)
Less than 12 months, Fair Value	226.5
Total, Unrealized Losses	(2.9)
Total, Fair Value	226.5
U.S. Government and Agencies Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Unrealized Losses	(2.3)
Less than 12 months, Fair Value	140.7
Total, Unrealized Losses	(2.3)
Total, Fair Value	140.7
Canadian and Provincial Government Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Unrealized Losses	(0.1)
Less than 12 months, Fair Value	7.0
Total, Unrealized Losses	(0.1)
Total, Fair Value	7.0
Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Unrealized Losses	(0.3)
Less than 12 months, Fair Value	23.5
Total, Unrealized Losses	(0.3)
Total, Fair Value	23.5
Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Fair Value	16.9
Total, Fair Value	16.9
Other Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Unrealized Losses	(0.2)
Less than 12 months, Fair Value	38.4
Total, Unrealized Losses	(0.2)
Total, Fair Value	$ 38.4