Defined Contribution Plans - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	May 31, 2016	May 31, 2015	May 31, 2014
401(k) Savings
Defined Contribution Plan Disclosure [Line Items]
Required years of service for plan eligibility (years)	1 year
Defined contribution plan, total contributions	$ 43.1	$ 38.4	$ 33.7
Deferred Profit Sharing Plan (DPSP)
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, total contributions	1.6	1.5	1.6
Supplemental Executive Retirement Plan (SERP)
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, total contributions	$ 6.6	$ 6.1	$ 6.0