Stock-Based Compensation Plans (Weighted-Average Assumptions) (Details) - $ / shares	12 Months Ended
May 31, 2016	May 31, 2015	May 31, 2014
Performance Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate			1.50%
Dividend yield			3.90%
Volatility factor			0.20%
Expected option life in years			4 years 6 months
Weighted-average grant-date fair value of stock options granted (per share)			$ 3.85
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	1.90%	2.10%	2.00%
Dividend yield	3.60%	3.70%	4.10%
Volatility factor	0.18%	0.21%	0.22%
Expected option life in years	6 years 1 month 6 days	6 years	6 years 4 months 24 days
Weighted-average grant-date fair value of stock options granted (per share)	$ 5.25	$ 5.68	$ 4.90

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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- Definition

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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- Definition

The risk-free interest rate assumption that is used in valuing an option on its own shares.

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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.

+ References

No definition available.

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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- Definition

Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(i)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.D.2)
-URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809

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