Defined Contribution Plans (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	May 31, 2012	May 31, 2011	May 31, 2010
401(k) [Member]
Defined Benefit Plan Disclosure [Line Items]
Total contributions to defined benefit plans	$ 26.0	$ 21.1	$ 19.8
Deferred Profit Sharing Plan (DPSP) [Member]
Defined Benefit Plan Disclosure [Line Items]
Total contributions to defined benefit plans	1.3	1.0	0.9
Supplemental Executive Retirement Plan (SERP) [Member]
Defined Benefit Plan Disclosure [Line Items]
Total contributions to defined benefit plans	$ 5.7	$ 6.1	$ 5.0