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Employee Benefit Plans - Narrative (Details) - Pension Plans - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Nov. 30, 2017
Nov. 30, 2016
Nov. 30, 2017
Nov. 30, 2016
United States        
Employee Benefit Plans (Details) [Line Items]        
Pension contributions     $ 0.0  
Short-term expected rate of return     4.75%  
Discount rate     2.20%  
Lump sum benefit payments made     $ 37.4  
Benefit cost of settlement event $ (15.4) $ 0.0 (15.4) $ 0.0
United Kingdom        
Employee Benefit Plans (Details) [Line Items]        
Pension contributions     0.6  
Contributions expected in current fiscal year 1.1   1.1  
Benefit cost of settlement event $ 0.0 $ 0.0 $ 0.0 $ 0.0