Employee Benefit Plans (Details) - USD ($) $ in Millions	12 Months Ended
	May 31, 2017	May 31, 2016	May 31, 2015
Cash balance pension plan
Employee benefit plans
Interest crediting rate as a percentage of average 30-year treasury rate	100.00%
Average period of treasury rate used in determination of interest crediting rate	30 years
Average interest crediting rate (as a percent)	4.50%
Defined Benefit Pension Plans
Change in projected benefit obligation:
Projected benefit obligation at beginning of year	$ 145.7	$ 144.9
Service cost	2.5	2.5
Interest cost	4.2	4.5
Participant contributions	0.3	0.3
Net actuarial gain	(2.0)	(1.1)
Benefit payments	(6.0)	(6.0)
Foreign currency translation adjustment	0.7	0.6
Projected benefit obligation at end of year	145.4	145.7	$ 144.9
Change in the fair value of plan assets:
Fair value of plan assets at beginning of year	111.0	115.8
Actual return on plan assets	9.9	(3.0)
Employer contributions	2.9	3.4
Participant contributions	0.3	0.3
Benefit payments	(6.0)	(6.0)
Foreign currency translation adjustment	0.7	0.5
Fair value of plan assets at end of year	118.8	111.0	115.8
Funded status at end of year	(26.6)	(34.7)
Amounts recognized in the consolidated balance sheets
Accrued liabilities	(2.7)	(3.8)
Other liabilities and deferred income	(23.9)	(30.9)
Funded status at end of year	(26.6)	(34.7)
Amounts recognized in accumulated other comprehensive loss
Actuarial loss		58.8	66.4
Prior service credit		(0.4)	(0.4)
Total		58.4	66.0
Accumulated benefit obligation	140.0
Net Periodic Benefit Cost
Service cost	2.5	2.5	2.0
Interest cost	4.2	4.5	4.8
Expected return on plan assets	(6.5)	(6.5)	(6.0)
Curtailment			0.2
Amortization of prior service cost		0.1	0.2
Recognized net actuarial loss	2.4	2.4	1.8
Total	2.6	$ 3.0	$ 3.0
Estimated amounts that will be amortized from accumulated other comprehensive loss into expense over the next fiscal year
Net actuarial loss	2.3
Total	$ 2.3
Defined Benefit Pension Plans | Board of Directors
Employee benefit plans
Benefits paid in cash as percentage of the annual retainer fees payable to active outside director	25.00%
Defined Benefit Pension Plans | Minimum | Board of Directors
Employee benefit plans
Minimum age of retirement	65 years
Required minimum years of service as a director	5 years
Defined Benefit Pension Plans | Maximum | Board of Directors
Employee benefit plans
Period for which benefits will be payable	10 years
Domestic plans
Key weighted-average assumptions used in the measurement of the company's projected benefit obligations
Discount rate (as a percent)	3.82%	3.83%
Rate of compensation increase (as a percent)	2.50%	2.50%
Weighted-average assumptions used to determine net periodic pension expense
Discount rate: (as a percent)	3.83%	4.15%	4.23%
Rate of compensation increase: (as a percent)	2.50%	2.50%	2.50%
Expected long-term rate on plan assets: (as a percent)	7.25%	7.25%	7.50%
Plan Assets
Actual asset allocation (as a percent)	100.00%	100.00%
Domestic plans | Equity securities
Plan Assets
Actual asset allocation (as a percent)	62.00%	59.00%
Domestic plans | Fixed income securities
Plan Assets
Actual asset allocation (as a percent)	16.00%	17.00%
Domestic plans | Other
Plan Assets
Actual asset allocation (as a percent)	22.00%	24.00%
Domestic plans | Minimum | Equity securities
Plan Assets
Target Asset Allocation (as a percent)	45.00%
Domestic plans | Minimum | Fixed income securities
Plan Assets
Target Asset Allocation (as a percent)	15.00%
Domestic plans | Minimum | Other
Plan Assets
Target Asset Allocation (as a percent)	0.00%
Domestic plans | Maximum | Equity securities
Plan Assets
Target Asset Allocation (as a percent)	75.00%
Domestic plans | Maximum | Fixed income securities
Plan Assets
Target Asset Allocation (as a percent)	25.00%
Domestic plans | Maximum | Other
Plan Assets
Target Asset Allocation (as a percent)	25.00%
International plans
Key weighted-average assumptions used in the measurement of the company's projected benefit obligations
Discount rate (as a percent)	2.00%	1.90%
Rate of compensation increase (as a percent)	3.00%	3.00%
Weighted-average assumptions used to determine net periodic pension expense
Discount rate: (as a percent)	1.90%	1.90%	1.90%
Rate of compensation increase: (as a percent)	3.00%	3.00%	3.00%
Expected long-term rate on plan assets: (as a percent)	4.00%	4.00%	4.00%