Annual report pursuant to Section 13 and 15(d)

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

v3.7.0.1
Accumulated Other Comprehensive Income (Changes in Accumulated Other Comprehensive Income) (Details) - USD ($)
$ in Millions
12 Months Ended
May 31, 2017
May 31, 2016
May 31, 2015
Accumulated Other Comprehensive Income [Abstract]      
Beginning balance $ 29.2 $ 7.5 $ 21.5
Unrealized holding (losses)/gains (14.7) 34.2 (21.5)
Income tax benefit/(expense) related to unrealized holding (losses)/gains 5.6 (12.4) 7.7
Reclassification adjustment for the net gain on sale of available-for-sale securities realized in net income (0.1) (0.1) (0.3)
Income tax expense on reclassification adjustment for the net gain on sale of available-for-sale securities 0.1
Total other comprehensive (loss)/income, net of tax (9.2) 21.7 (14.0)
Ending balance 20.0 29.2 7.5
Total tax (benefit)/expense included in other comprehensive (loss)/income $ (5.6) $ 12.4 $ (7.8)