Summary of Significant Accounting Policies - Revenue Recognition (Details) - USD ($) $ in Millions	12 Months Ended
May 31, 2018	May 31, 2017	May 31, 2016
Revenue Recognition
Recognized net favorable cumulative catch-up adjustments	$ 3.6	$ 8.5	$ 3.7
KC10 logistics support services
Revenue Recognition
Sales for KC10 logistics support services	29.1	110.6	148.1
Gross profit recognized for KC10 logistics support services	$ 4.8	$ 8.7	$ 16.0
Minimum
Principles of Consolidation
Percentage of owned aircraft	20.00%
Maximum
Principles of Consolidation
Percentage of owned aircraft	50.00%

Average annual gross profit recognized for KC10 logistics support services.

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Amount of recognized favorable cumulative catch-up adjustments under revenue recognition.

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Sales revenue recognized for KC10 logistics support services.

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33918-111571

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