Short-term Financing (Lines of Credit Facility Amount Borrowed) (Details) - Revolving Credit Facility [Member] - USD ($) $ in Millions  | 
12 Months Ended | |
|---|---|---|
May 31, 2017  | 
May 31, 2016  | 
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| JP Morgan Chase Bank, N.A. [Member] | ||
| Line of Credit Facility [Line Items] | ||
| Number of days borrowed | 30 days | 5 days | 
| Maximum amount borrowed | $ 450.0 | $ 450.0 | 
| Weighted-average amount borrowed | $ 196.7 | $ 305.0 | 
| Weighted-average interest rate | 2.89% | 3.39% | 
| PNC Bank, National Association [Member] | ||
| Line of Credit Facility [Line Items] | ||
| Number of days borrowed | 353 days | |
| Maximum amount borrowed | $ 55.6 | |
| Weighted-average amount borrowed | $ 52.8 | |
| Weighted-average interest rate | 1.21% | |
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- Definition Line of Credit Facility, Number Of Days Borrowed No definition available. 
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- Definition Average amount borrowed under the credit facility during the period. No definition available. 
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- Definition The effective interest rate during the reporting period. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition 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. No definition available. 
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- Definition Maximum amount borrowed under the credit facility at any time during the period. No definition available. 
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