Annual report pursuant to Section 13 and 15(d)

Income Taxes (Reconciliation of Gross Unrecognized Tax Benefits, Not Including Interest or Other Potential Offsetting Effects) (Details)

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Income Taxes (Reconciliation of Gross Unrecognized Tax Benefits, Not Including Interest or Other Potential Offsetting Effects) (Details) - USD ($)
$ in Millions
12 Months Ended
May 31, 2018
May 31, 2017
May 31, 2016
Income Taxes [Abstract]      
Balance as of beginning of fiscal year $ 43.7 $ 64.7 $ 39.9
Additions for tax positions of the current year 2.3 8.2 7.3
Additions for tax positions of prior years 0.1 4.8 20.7
Reductions for tax positions of prior years (1.2) (2.5) (0.1)
Settlements with tax authorities (28.6) (29.5) (2.2)
Expiration of the statute of limitations (1.4) (2.0) (0.9)
Balance as of end of fiscal year $ 14.9 $ 43.7 $ 64.7