Share-based Payments (Details 3) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	May 31, 2013	May 31, 2012
A summary of the status of the Companys restricted stock units at May 31 is presented below:
The average weighted-average period the unrecognized compesation cost will be recognized (years)	1 year 10 months 24 days
Restricted Stock Units R S U [Member]
A summary of the status of the Companys restricted stock units at May 31 is presented below:
Number of stock units outstanding at beginning of period (shares)	0.6
Granted (shares)	0.3
Issued and canceled (shares)	0.2
Number of stock units outstanding at end of period (shares)	0.7
Weighted-average grant date fair value per share - stock unit awards outstanding, beginning of period	$ 54.47
Granted	$ 57.36
Issued and canceled	$ 53.20
Weighted-average grant date fair value per share - stock unit awards outstanding, end of period	$ 56.40
Performance Stock Unit [Member]
A summary of the status of the Companys restricted stock units at May 31 is presented below:
Number of stock units outstanding at beginning of period (shares)	0.1
Granted (shares)	0.1
Issued and canceled (shares)	0
Number of stock units outstanding at end of period (shares)	0.2	0.1
Weighted-average grant date fair value per share - stock unit awards outstanding, beginning of period	$ 81.10
Granted	$ 71.19
Issued and canceled	$ 0
Weighted-average grant date fair value per share - stock unit awards outstanding, end of period	$ 75.15	$ 81.10
Expected volatility (percent)	38.05%	54.72%
Expected dividend yield (percent)	1.74%	0.28%
Expected term (in years)	3 years	3 years
Risk-free interest rate (percent)	0.31%	0.69%