Defined Contribution Plans - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	May. 31, 2015	May. 31, 2014	May. 31, 2013
401(k) Savings
Defined Benefit Plan Disclosure [Line Items]
Required years of service for plan eligibility (years)	1 year
Total contributions to defined benefit plans	$ 38.4	$ 33.7	$ 28.4
Deferred Profit Sharing Plan (DPSP)
Defined Benefit Plan Disclosure [Line Items]
Total contributions to defined benefit plans	1.5	1.6	1.4
Supplemental Executive Retirement Plan (SERP)
Defined Benefit Plan Disclosure [Line Items]
Total contributions to defined benefit plans	$ 6.1	$ 6.0	$ 4.7