Customer Trust Fund - Investment of Customer Trust Fund (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Money market securities, investments carried at cost and other cash equivalents, Fair Value	$ 1,872.4	$ 1,348.1
Invested customer trust funds, Fair Value	3,632.9	3,174.9
Trust receivables, Fair Value	16.6	29.2	[1]
Total customer trust funds, Fair Value	3,649.5	3,204.1
Money market securities, investments carried at cost and other cash equivalents, Amortized Cost	1,872.4	1,348.1
Invested customer trust funds, Amortized Cost	3,588.6	3,153.2
Trust receivables, Amortized Cost	16.6	40.4
Total customer trust funds, Amortized Cost	3,605.2	3,193.6
Amortized Cost	1,716.2	1,805.1
Gross Unrealized Gain	45.6	23.4
Gross Unrealized Loss	(1.3)	(1.7)
Fair value	1,760.5	1,826.8
U.S. Government and Agencies Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	542.3	542.4
Gross Unrealized Gain	22.9	7.1
Gross Unrealized Loss		(0.3)
Fair value	565.2	549.2
Canadian and Provincial Government Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	375.2	406.7
Gross Unrealized Gain	11.3	5.4
Gross Unrealized Loss		(0.7)
Fair value	386.5	411.4
Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	529.8	562.2
Gross Unrealized Gain	9.3	9.0
Gross Unrealized Loss	(0.5)	(0.3)
Fair value	538.6	570.9
Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	247.0	270.0
Gross Unrealized Gain	1.8	1.7
Gross Unrealized Loss	(0.8)	(0.3)
Fair value	248.0	271.4
Mortgage-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	17.9	19.8
Gross Unrealized Gain	0.3	0.2
Gross Unrealized Loss		(0.1)
Fair value	18.2	19.9
Other Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4.0	4.0
Fair value	$ 4.0	$ 4.0

[1] The fair value of trust receivables as of December 31, 2019, includes a loss of $11.2 million related to unrecovered duplicate payments resulting from the September 26, 2019, isolated service incident.  Ceridian is liable for these unrecovered duplicate payments and has reimbursed the customer trust for the resulting losses as of March 31, 2020.  Please refer to Note 13, “Commitments and Contingencies,” for further discussion of the September 26, 2019, isolated service incident.