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 6 Months Ended
Nov. 30, 2013
Nov. 30, 2012
Nov. 30, 2013
Nov. 30, 2012
Equity [Abstract]        
Accumulated other comprehensive income/(loss),Beginning balance $ (4.9) $ 37.3 $ 22.0 $ 37.7
Other comprehensive income/(loss):        
Unrealized gains/(losses) on available-for-sale securities, net of tax 18.6 2.5 (8.2) 2.2
Reclassification adjustment for the net gain on sale of available-for-sale securities realized in net income, net of tax 0 (0.1) (0.1) (0.2)
Total other comprehensive income/(loss), net of tax 18.6 2.4 (8.3) 2.0
Accumulated other comprehensive income/(loss),Ending balance 13.7 39.7 13.7 39.7
Accumulated Other Comprehensive Income/(Loss) (Textual)        
Other comprehensive income/(loss), tax expense/(benefit) $ 10.8 $ 1.6 $ (4.8) $ 1.3