Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	May 31, 2017	Feb. 29, 2016	May 31, 2017	May 31, 2016	May 31, 2015
Current:
Federal			$ 20.2	$ 10.6	$ 11.4
State			0.2	0.4	0.4
Foreign			3.1	3.8	1.5
Total current			23.5	14.8	13.3
Deferred			0.6	4.8	(52.6)
Provision for income tax (benefit)			$ 24.1	$ 19.6	$ (39.3)
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 tax (benefit) at the federal statutory rate			$ 26.0	$ 20.3	$ (39.6)
State income taxes, net of federal benefit and refunds			0.2	0.2	0.2
Federal adjustments			0.1	0.4	0.1
State net operating losses			(5.7)	(1.1)	(0.1)
Valuation allowance for state deferred tax assets			5.7	1.1	0.1
Prior period adjustments				(1.3)
Effective settlement of prior tax position			2.2
Provision for income tax (benefit)			24.1	19.6	(39.3)
Income tax expense in discontinued operations	$ (6.7)	$ 2.8
Income tax expense in continued operations			24.1	19.6	(39.3)
Income (Loss) before provision for income tax (benefit)			74.3	57.9	(113.2)
Deferred tax assets:
Inventory costs	21.3		21.3	19.9
Impairments	5.6		5.6	9.4
Advanced billings	1.7		1.7	11.1
Postretirement benefits	6.8		6.8	12.0
Employee benefits	12.3		12.3	10.0
State NOLs, tax credits and incentives	9.4		9.4	6.5
Other	1.7		1.7	0.6
Total deferred tax assets	58.8		58.8	69.5
Valuation allowance	(10.4)		(10.4)	(4.7)
Total deferred tax assets net of valuation allowance	48.4		48.4	64.8
Deferred tax liabilities:
Tangible and intangible assets	(85.5)		(85.5)	(99.0)
Other	(0.1)		(0.1)	(0.1)
Total deferred tax liabilities	(85.6)		(85.6)	(99.1)
Net deferred tax liabilities	(37.2)		(37.2)	(34.3)
Reconciliation of unrecognized tax benefits
Beginning balance			12.9	2.2	2.2
Additions for tax positions of prior years			0.4	10.7
Effective settlement of prior tax position			(8.9)
End balance	4.4		$ 4.4	12.9	2.2
Unrecognized tax benefit resulting from statute lapse	2.2
Minimum
Deferred tax liabilities:
Period for net operating losses carry forward (in years)			5 years
Maximum
Deferred tax liabilities:
Period for net operating losses carry forward (in years)			20 years
Accrued Liabilities
Deferred tax liabilities:
Income tax payable	$ 12.3		$ 12.3	1.1
Domestic
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
Income (Loss) before provision for income tax (benefit)			54.9	44.7	(124.4)
Foreign
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
Income (Loss) before provision for income tax (benefit)			$ 19.4	$ 13.2	$ 11.2
Immaterial errors
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
Accrued Income Taxes		0.2
Corrections
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
Income tax expense in discontinued operations		1.5
Income tax expense in continued operations		$ 1.3