Description of Business, Basis of Presentation, and Significant Accounting Policies (Narrative) (Details) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Nov. 30, 2022 USD ($) Item	Nov. 30, 2021 USD ($) Item	Nov. 30, 2022 USD ($) Segment Item	Nov. 30, 2021 USD ($) Item	May 31, 2023 USD ($)	May 31, 2022 USD ($) Item
Accounting Policies [Line Items]
Number of reportable segments | Segment			1
Allowance for credit losses	$ 20.4		$ 20.4			$ 18.2
Advance collections	34.4		34.4			2.6
Maximum individual health insurance claims liability						0.5
Stock-based compensation costs recognized	$ 15.3	$ 14.0	$ 29.7	$ 26.4
Accounting Standards Update 2021-10 [Member]
Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adoption date	Jun. 01, 2022		Jun. 01, 2022
Change in accounting principle, accounting standards update, adopted [true false]	true		true
Change in accounting principle, accounting standards update, immaterial effect [true false]	true		true
Forecast [Member]
Accounting Policies [Line Items]
Maximum individual health insurance claims liability					$ 0.5
Trade Receivables [Member]
Accounting Policies [Line Items]
Receivables	$ 277.1		$ 277.1			123.2
Purchased Receivables [Member]
Accounting Policies [Line Items]
Receivables	$ 616.9		$ 616.9			$ 618.8
Accounts And Unbilled Receivables [Member]
Accounting Policies [Line Items]
Number of clients creating a credit concentration | Item			0			0
Revenue [Member]
Accounting Policies [Line Items]
Number of clients creating a credit concentration | Item	0	0	0	0
PEO [Member]
Accounting Policies [Line Items]
Individual workers' compensation claims liability						$ 1.0
PEO [Member] | Forecast [Member]
Accounting Policies [Line Items]
Individual workers' compensation claims liability					1.0
PEO Aggregate Claims Exceeding $1.0M [Member] | Minimum [Member]
Accounting Policies [Line Items]
Individual workers' compensation claims liability						1.0
PEO Aggregate Claims Exceeding $1.0M [Member] | Minimum [Member] | Forecast [Member]
Accounting Policies [Line Items]
Individual workers' compensation claims liability					1.0
PEO Aggregate Claims Exceeding $1.0M [Member] | Maximum [Member]
Accounting Policies [Line Items]
Maximum individual workers' compensation claims liability						$ 2.0
PEO Aggregate Claims Exceeding $1.0M [Member] | Maximum [Member] | Forecast [Member]
Accounting Policies [Line Items]
Maximum individual workers' compensation claims liability					$ 2.0