Customer Trust Fund - Investment of Customer Trust Fund (Detail) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Money market securities, investments carried at cost and other cash equivalents, Fair Value	$ 985.9	$ 1,348.1
Invested customer trust funds, Fair Value	2,631.6	3,174.9
Trust receivables, Fair Value	28.2	29.2	[1]
Total customer trust funds, Fair Value	2,659.8	3,204.1
Money market securities, investments carried at cost and other cash equivalents, Amortized Cost	985.9	1,348.1
Invested customer trust funds, Amortized Cost	2,566.7	3,153.2
Trust receivables, Amortized Cost	28.1	40.4
Total customer trust funds, Amortized Cost	2,594.8	3,193.6
Amortized Cost	1,580.8	1,805.1
Gross Unrealized Gain	65.0	23.4
Gross Unrealized Loss	(0.1)	(1.7)
Fair value	1,645.7	1,826.8
U.S. Government and Agencies Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	482.1	542.4
Gross Unrealized Gain	24.5	7.1
Gross Unrealized Loss		(0.3)
Fair value	506.6	549.2
Canadian and Provincial Government Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	376.6	406.7
Gross Unrealized Gain	16.4	5.4
Gross Unrealized Loss		(0.7)
Fair value	393.0	411.4
Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	481.0	562.2
Gross Unrealized Gain	18.8	9.0
Gross Unrealized Loss	(0.1)	(0.3)
Fair value	499.7	570.9
Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	221.8	270.0
Gross Unrealized Gain	4.9	1.7
Gross Unrealized Loss		(0.3)
Fair value	226.7	271.4
Mortgage-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	15.4	19.8
Gross Unrealized Gain	0.3	0.2
Gross Unrealized Loss		(0.1)
Fair value	15.7	19.9
Other Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3.9	4.0
Gross Unrealized Gain	0.1
Fair value	$ 4.0	$ 4.0

[1] The fair value of trust receivables as of December 31, 2019, included a loss of $11.2 million related to unrecovered duplicate payments resulting from an isolated service incident on September 26, 2019. Ceridian was liable for these unrecovered duplicate payments and had reimbursed the customer trust for the resulting losses as of March 31, 2020. Please refer to Note 14, “Commitments and Contingencies,” for further discussion of the September 26, 2019, isolated service incident.