Quarterly report pursuant to Section 13 or 15(d)

Accumulated Other Comprehensive Income/(Loss) (Details)

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Accumulated Other Comprehensive Income/(Loss) (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Aug. 31, 2014
Aug. 31, 2013
Equity [Abstract]    
Accumulated other comprehensive income/(loss), Beginning balance $ 21.5 $ 22.0
Other comprehensive income/(loss):    
Unrealized gains/(losses) on available-for-sale securities, net of tax 4.6 (26.8)
Reclassification adjustment for the net gain on sale of available-for-sale securities realized in net income, net of tax (0.1) (0.1)
Total other comprehensive income/(loss), net of tax 4.5 (26.9)
Accumulated other comprehensive income/(loss), Ending balance 26.0 (4.9)
Accumulated Other Comprehensive Income/(Loss) (Textual)    
Other comprehensive income/(loss), tax expense/(benefit) $ 2.1 $ (15.6)