Business Segment Information - Sales and Gross Profit (Details) - USD ($) $ in Millions	12 Months Ended
	May 31, 2021	May 31, 2020	May 31, 2019
Disaggregation of revenue by major customer markets
Sales	$ 1,652.3	$ 2,072.0	$ 2,051.8
Gross profit	275.9	269.2	329.8
Aviation Services
Disaggregation of revenue by major customer markets
Sales	1,553.7	1,964.2	1,920.6
Gross profit	263.2	267.3	313.6
Aviation Services | Commercial
Disaggregation of revenue by major customer markets
Sales	793.9	1,268.9	1,342.3
Aviation Services | Government and defense
Disaggregation of revenue by major customer markets
Sales	759.8	695.3	578.3
Expeditionary Services
Disaggregation of revenue by major customer markets
Sales	98.6	107.8	131.2
Gross profit	12.7	1.9	16.2
Expeditionary Services | Commercial
Disaggregation of revenue by major customer markets
Sales	12.5	24.3	31.6
Expeditionary Services | Government and defense
Disaggregation of revenue by major customer markets
Sales	$ 86.1	$ 83.5	$ 99.6