Summary of Significant Accounting Policies - New Accounting Pronouncements Adopted (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	May 31, 2019	Feb. 28, 2019	Nov. 30, 2018	Aug. 31, 2018	May 31, 2018	Feb. 28, 2018	Nov. 30, 2017	Aug. 31, 2017	May 31, 2019	May 31, 2018	May 31, 2017	Jun. 01, 2018
New accounting pronouncements adopted
Excess income tax benefits									$ 4.9	$ 3.5	$ 25.1
Accounts receivable, net	$ 197.8				$ 202.0				197.8	202.0		$ 170.6
Inventories	523.7				460.7				523.7	460.7		443.4
Contract assets - current	59.2								59.2			49.6
Other current assets	36.2				26.2				36.2	26.2		25.3
Other non-current assets	77.5				118.9				77.5	118.9		99.9
Accrued liabilities	140.5				138.3				140.5	138.3		147.4
Deferred tax liabilities					15.7					15.7		9.1
Deferred revenue on long-term contracts	83.8				35.8				83.8	35.8		34.7
Retained earnings	709.8				733.2				709.8	733.2		712.8
Sales	562.7	$ 529.5	$ 493.3	$ 466.3	473.5	$ 456.3	$ 420.6	$ 397.9	2,051.8	1,748.3	1,590.8
Cost of sales									1,722.3
Operating income	29.3	29.8	16.8	22.4	22.8	24.3	21.8	17.1	98.3	86.0	82.3
Provision for income taxes									4.9	3.5	25.1
Income from continuing operations	26.6	27.4	11.2	18.9	18.1	31.3	13.3	11.0	84.1	73.7	52.0
Net Cash Provided by (Used in) Operating Activities, Continuing Operations [Abstract]
Net loss									7.5	15.6	56.5
Income from continuing operations	26.6	$ 27.4	$ 11.2	$ 18.9	18.1	$ 31.3	$ 13.3	$ 11.0	84.1	73.7	52.0
Accounts receivable									(34.4)	35.4	(16.8)
Contract assets									(9.7)
Inventories									(80.9)	(25.8)	(23.3)
Accrued and other liabilities									22.9	8.0	6.5
Other									21.6	(25.6)	$ (24.6)
Balances Excluding ASC 606
New accounting pronouncements adopted
Excess income tax benefits									4.9
Accounts receivable, net	236.3								236.3
Inventories	545.9								545.9
Other current assets	35.8								35.8
Other non-current assets	102.8								102.8
Accrued liabilities	134.5								134.5
Deferred tax liabilities	6.6								6.6
Deferred revenue on long-term contracts	89.0								89.0
Retained earnings	730.3								730.3
Sales									2,046.8
Cost of sales									1,717.2
Operating income									98.4
Provision for income taxes									4.9
Income from continuing operations									84.2
Net Cash Provided by (Used in) Operating Activities, Continuing Operations [Abstract]
Net loss									7.6
Income from continuing operations									84.2
Accounts receivable									(41.5)
Inventories									(85.8)
Accrued and other liabilities									26.1
Other									20.6
ASC 606 Adjustments
New accounting pronouncements adopted
Accounts receivable, net	38.5								38.5
Inventories	22.2								22.2
Contract assets - current	(59.2)								(59.2)
Other current assets	(0.4)								(0.4)
Other non-current assets	25.3								25.3
Accrued liabilities	(5.9)								(5.9)
Deferred tax liabilities	6.6								6.6
Deferred revenue on long-term contracts	5.2								5.2
Retained earnings	$ 20.5								20.5
Sales									(5.0)
Cost of sales									(5.1)
Operating income									0.1
Income from continuing operations									0.1
Net Cash Provided by (Used in) Operating Activities, Continuing Operations [Abstract]
Net loss									0.1
Income from continuing operations									0.1
Accounts receivable									(7.1)
Contract assets									9.7
Inventories									(4.9)
Accrued and other liabilities									3.2
Other									(1.0)
ASC 606 Adjustments | Other contracts
New accounting pronouncements adopted
Retained earnings												(22.1)
ASC 606 Adjustments | Repair services
New accounting pronouncements adopted
Retained earnings												1.3
ASC 606 Adjustments | Manufacturing products
New accounting pronouncements adopted
Retained earnings												$ 0.4
ASU 2016-09
New accounting pronouncements adopted
Excess income tax benefits									2.7	2.9
Provision for income taxes									2.7	2.9
ASU 2014-09
New accounting pronouncements adopted
Accounts receivable, net					202.0					202.0
Inventories					460.7					460.7
Other current assets					26.2					26.2
Other non-current assets					118.9					118.9
Accrued liabilities					138.3					138.3
Deferred tax liabilities					15.7					15.7
Deferred revenue on long-term contracts					35.8					35.8
Retained earnings					733.2					733.2
ASU 2014-09 | ASC 606 Adjustments
New accounting pronouncements adopted
Accounts receivable, net					(31.4)					(31.4)
Inventories					(17.3)					(17.3)
Contract assets - current					49.6					49.6
Other current assets					(0.9)					(0.9)
Other non-current assets					(19.0)					(19.0)
Accrued liabilities					9.1					9.1
Deferred tax liabilities					(6.6)					(6.6)
Deferred revenue on long-term contracts					(1.1)					(1.1)
Retained earnings					$ (20.4)					$ (20.4)
ASU 2017-07 | Other expense, net
New accounting pronouncements adopted
Pension income									$ 1.0