Summary of Significant Accounting Policies - Property, Plant and Equipment and Investments (Details) $ in Millions	12 Months Ended
May 31, 2020 USD ($)
Investments
Rotable asset impairment charges	$ 8.1
Future rent due to us under non-cancelable leases
2021	12.2
2022	11.6
2023	11.4
2024	11.3
2025	$ 11.3
Minimum
Future rent due to us under non-cancelable leases
Ownership interest in investee (as a percent)	20.00%
Maximum
Future rent due to us under non-cancelable leases
Ownership interest in investee (as a percent)	50.00%
Building and improvements \| Minimum
Property, Plant and Equipment
Useful life	10 years
Building and improvements \| Maximum
Property, Plant and Equipment
Useful life	40 years
Equipment \| Minimum
Property, Plant and Equipment
Useful life	3 years
Equipment \| Maximum
Property, Plant and Equipment
Useful life	10 years
Furniture and fixtures \| Minimum
Property, Plant and Equipment
Useful life	3 years
Furniture and fixtures \| Maximum
Property, Plant and Equipment
Useful life	10 years
Capitalized software \| Minimum
Property, Plant and Equipment
Useful life	3 years
Capitalized software \| Maximum
Property, Plant and Equipment
Useful life	10 years
Rotable assets
Investments
Rotable asset impairment charges	$ 1.9

Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

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