Stock-Based Compensation Plans (Details 3) (Employee Stock Option [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
May 31, 2013	May 31, 2012	May 31, 2011
Employee Stock Option [Member]
Stock options, other information
Total intrinsic value of stock options exercised	$ 7.8	$ 0.8	$ 1.9
Total grant-date fair value of stock options vested	$ 3.0	$ 10.4	$ 20.0

The total accumulated difference between fair values of underlying shares on dates of exercise and exercise price on options which were exercised (or share units converted) into shares during the reporting period under the plan.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (d)(2)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph c(2)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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