Business Segment Information - Geographic Data (Details) - USD ($) $ in Millions	12 Months Ended
	May 31, 2021	May 31, 2020	May 31, 2019
Business Segment Information
Net sales	$ 1,652.3	$ 2,072.0	$ 2,051.8
Long-lived assets	602.7	640.3
United States
Business Segment Information
Long-lived assets	419.1	423.9
Europe
Business Segment Information
Long-lived assets	83.1	102.1
Other
Business Segment Information
Long-lived assets	100.5	114.3
Foreign countries
Business Segment Information
Net sales	$ 370.5	$ 591.8	$ 661.8
Foreign countries | Total sales | Geographic concentration
Business Segment Information
Percentage of total sales	22.40%	28.60%	32.30%
Aviation Services
Business Segment Information
Net sales	$ 1,553.7	$ 1,964.2	$ 1,920.6
Aviation Services | North America
Business Segment Information
Net sales	1,255.7	1,505.6	1,426.8
Aviation Services | Europe
Business Segment Information
Net sales	207.5	330.8	323.4
Aviation Services | Other
Business Segment Information
Net sales	90.5	127.8	170.4
Expeditionary Services
Business Segment Information
Net sales	98.6	107.8	131.2
Expeditionary Services | North America
Business Segment Information
Net sales	95.9	98.4	124.1
Expeditionary Services | Europe
Business Segment Information
Net sales	2.6	9.0	5.8
Expeditionary Services | Other
Business Segment Information
Net sales	$ 0.1	$ 0.4	$ 1.3