Annual report pursuant to Section 13 and 15(d)

Accumulated Other Comprehensive (Loss)/ Income (Changes in Accumulated Other Comprehensive (Loss)/Income) (Details)

v3.10.0.1
Accumulated Other Comprehensive (Loss)/ Income (Changes in Accumulated Other Comprehensive (Loss)/Income) (Details) - USD ($)
$ in Millions
12 Months Ended
May 31, 2018
May 31, 2017
May 31, 2016
Accumulated Other Comprehensive (Loss)/Income [Abstract]      
Beginning balance $ 20.0 $ 29.2 $ 7.5
Unrealized holding (losses)/gains (70.2) (14.7) 34.2
Income tax benefit/(expense) related to unrealized holding (losses)/gains 22.6 5.6 (12.4)
Reclassification adjustment for the net gain on sale of available-for-sale securities realized in net income (0.1) (0.1)
Foreign currency translation adjustment (8.6)
Total other comprehensive (loss)/income, net of tax (56.2) (9.2) 21.7
Ending balance (36.2) 20.0 29.2
Total tax (benefit)/expense included in other comprehensive (loss)/income $ (22.6) $ (5.6) $ 12.4