Funds Held for Clients and Corporate Investments (Narrative) (Details) $ in Millions	12 Months Ended
May 31, 2016 USD ($) security	May 31, 2015 USD ($) security
Schedule of Available-for-sale Securities [Line Items]
Net unrealized gain on available-for-sale securities	$ 47.6	$ 13.6
Number of available-for-sale securities in an unrealized loss position \| security	63	280
Gross unrealized losses on available-for-sale securities	$ 0.7	$ 7.5
Variable Rate Demand Notes [Member] \| Minimum [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities contractual maturities	20 years
Variable Rate Demand Notes [Member] \| Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities contractual maturities	30 years

Available-for-sale Securities, Debt Maturities, Term

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Amount before tax of unrealized gain (loss) in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

No definition available.

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- Definition

Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale in a continuous loss position.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27337-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27290-111563

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- Definition

Number of investment positions in available-for-sale investments in a continuous unrealized loss position for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27290-111563

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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