| Goodwill and Intangible Assets, Net of Accumulated Amortization (Components of Intangible Assets, at Cost) (Details) - USD ($) $ in Millions | May 31, 2020 | May 31, 2019 | 
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| Intangible Assets [Line Items] | ||
| Total intangible assets, gross | $ 641.7 | $ 631.2 | 
| Less: Accumulated amortization | 311.1 | 232.1 | 
| Intangible assets, net of accumulated amortization | 330.6 | 399.1 | 
| Other Intangible Assets [Member] | ||
| Intangible Assets [Line Items] | ||
| Total intangible assets, gross | 23.3 | 23.0 | 
| Client Lists [Member] | ||
| Intangible Assets [Line Items] | ||
| Total intangible assets, gross | $ 618.4 | $ 608.2 | 
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- Definition Intangible Assets [Line Items] No definition available. 
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- Definition Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
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- Definition Amount before accumulated amortization of intangible assets, excluding goodwill. No definition available. 
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- Definition Sum of the carrying amounts of all intangible assets, excluding goodwill, as of the balance sheet date, net of accumulated amortization and impairment charges. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- Details 
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- Details 
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