Quarterly report pursuant to Section 13 or 15(d)

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

v3.8.0.1
Accumulated Other Comprehensive (Loss)/ Income (Changes in Accumulated Other Comprehensive (Loss)/Income) (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Feb. 28, 2018
Feb. 28, 2017
Feb. 28, 2018
Feb. 28, 2017
Accumulated Other Comprehensive (Loss)/Income [Abstract]        
Beginning balance $ (9.2) $ (16.8) $ 20.0 $ 29.2
Unrealized (losses)/gains on available-for-sale securities, net of tax (17.5) 21.4 (46.7) (24.6)
Total other comprehensive (loss)/income, net of tax (17.5) 21.4 (46.7) (24.6)
Ending balance (26.7) 4.6 (26.7) 4.6
Total tax (benefit)/expense included in other comprehensive income $ (3.2) $ 12.3 $ (20.1) $ (14.0)