Description of Business, Basis of Presentation, and Significant Accounting Policies (Narrative) (Details) $ in Millions		3 Months Ended		9 Months Ended		12 Months Ended
	Jun. 01, 2019 USD ($)	Feb. 29, 2020 USD ($)	Feb. 28, 2019 USD ($)	Feb. 29, 2020 USD ($) segment	Feb. 28, 2019 USD ($)	May 31, 2020 USD ($)	May 31, 2019 USD ($)
Accounting Policies [Line Items]
Number of reportable segments | segment				1
Allowance for doubtful accounts		$ 12.1		$ 12.1			$ 7.5
Advance collections		8.1		8.1			4.2
Maximum individual health insurance claims liability							0.3
Operating lease, impairment loss				0.0
Stock-based compensation costs recognized		12.7	$ 10.8	36.5	$ 33.6
Operating lease, right-of-use asset		124.3		124.3
Operating lease, liability		142.7		142.7
Forecast [Member]
Accounting Policies [Line Items]
Maximum individual workers' compensation claims liability						$ 1.0
Maximum individual health insurance claims liability						$ 0.3
ASU 2016-02 [Member]
Accounting Policies [Line Items]
Increase in lease-related assets and liabilities	$ 116.4
Operating lease, right-of-use asset	116.4
Operating lease, liability	135.3
Unamortized landlord allowances and lease incentives	$ 18.9
Trade Receivables [Member]
Accounting Policies [Line Items]
Receivables		98.7		98.7			94.5
Purchased Receivables [Member]
Accounting Policies [Line Items]
Receivables		$ 349.7		$ 349.7			333.5
Minimum [Member]
Accounting Policies [Line Items]
Maximum individual workers' compensation claims liability							0.5
Maximum [Member]
Accounting Policies [Line Items]
Maximum individual workers' compensation claims liability							$ 1.0
Europe [Member] | Revenue [Member] | Geographic Concentration Risk [Member]
Accounting Policies [Line Items]
Total percentage		1.00%	1.00%	1.00%	1.00%
Europe [Member] | Long Lived Assets [Member] | Geographic Concentration Risk [Member]
Accounting Policies [Line Items]
Total percentage				5.00%			5.00%