Income Taxes (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	May 31, 2014	May 31, 2013	May 31, 2012
Current:
Federal	$ (0.5)	$ (13.1)	$ (9.8)
State	0.2	(1.8)	(0.5)
Foreign	22.8	12.1	3.0
Total current	22.5	(2.8)	(7.3)
Deferred	9.6	29.5	32.8
Provision for income taxes	32.1	26.7	25.5
Income tax receivable	14.8	18.0
U.S. federal statutory income tax rate (as a percent)	35.00%	35.00%	35.00%
Reasons for difference between the provision for income taxes on pre-tax income from the amount computed by applying the U.S. federal statutory tax rate
Provision for income taxes at the federal statutory rate	36.9	28.8	32.7
State income taxes, net of federal benefit and refunds	0.2	(1.0)	(3.5)
Federal adjustments	(2.2)		(3.3)
Domestic Production Activities Deduction	(1.6)
Research and development credit	(1.0)	(1.1)	(0.8)
Noncontrolling interest	(0.1)	(0.2)	(0.1)
Other	(0.1)	0.2	0.5
Provision for income taxes	32.1	26.7	25.5
Deferred tax assets-current attributable to:
Inventory costs	14.4	14.8
Employee benefits	7.9	8.3
Allowance for doubtful accounts	0.8	1.6
Advanced billings and other	7.0	(6.7)
Total net deferred tax assets-current	30.1	18.0
Deferred tax assets-noncurrent attributable to:
Postretirement benefits	17.6	17.7
Bond hedge	0.8	1.7
Foreign intangible assets	37.5	41.5
AMT, NOL and FTC carrybacks	20.6	37.6
Other	3.0	1.0
Total deferred tax assets-noncurrent	79.5	99.5
Total deferred tax assets	109.6	117.5
Deferred tax liabilities attributable to:
Depreciation	(166.9)	(163.5)
Convertible notes	(2.1)	(3.9)
Capitalized program development costs	(34.1)	(28.8)
Foreign intangible assets	(37.5)	(41.5)
Other	(1.1)
Total deferred tax liabilities	(241.7)	(237.7)
Net deferred tax liabilities	(132.1)	(120.2)
Effective income tax rate (as a percent)	30.50%	32.50%	27.20%
Reduction in income tax expense related to tax provision to federal income tax return filing differences	2.7
Domestic Production Activities Deduction	(1.6)
Reduction in income tax expense related to reduction of the entity's state income tax rate		$ 1.3	$ 4.0