Income Taxes (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	May 31, 2016	May 31, 2015
Income Tax Contingency [Line Items]
Reserve for uncertain tax positions	$ 54.2	$ 29.1
Impact of uncertain tax positions, if recognized, on effective income tax rate	$ 54.2	$ 29.1
Federal [Member] | IRS [Member] | Earliest Tax Year [Member]
Income Tax Contingency [Line Items]
Fiscal year currently under audit	2012
Fiscal years subject to potential audit	2015
Federal [Member] | IRS [Member] | Latest Tax Year [Member]
Income Tax Contingency [Line Items]
Fiscal year currently under audit	2014
Fiscal years subject to potential audit	2016