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           Income Taxes (Details) (USD $) 
        In Millions, unless otherwise specified  | 
        
           May 31, 2013 
         | 
        
           May 31, 2012 
         | 
      
|---|---|---|
| Deferred tax assets: | ||
| Compensation and employee benefit liabilities | $ 16.3 | $ 15.8 | 
| Other current liabilities | 6.3 | 6.7 | 
| Tax credit carry forward | 35.3 | 31.7 | 
| Depreciation | 8.5 | 8.0 | 
| Stock-based compensation | 24.6 | 28.5 | 
| Other | 16.6 | 17.4 | 
| Gross deferred tax assets | 107.6 | 108.1 | 
| Deferred tax liabilities: | ||
| Capitalized software | 45.8 | 39.3 | 
| Depreciation | 20.2 | 21.8 | 
| Intangible assets | 41.0 | 36.8 | 
| Revenue not subject to current taxes | 11.7 | 11.1 | 
| Unrealized gains on available-for-sale securities | 13.3 | 21.8 | 
| Other | 0.6 | 1.0 | 
| Gross deferred tax liabilities | 132.6 | 131.8 | 
| Net deferred tax liability | $ (25.0) | $ (23.7) | 
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- Details 
          
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- Definition 
          Amount before allocation of valuation allowances of deferred tax liability to taxable temporary differences. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition 
          Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition 
          Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences not separately disclosed. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition 
          Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from property, plant, and equipment. No definition available. 
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- Definition 
          The tax effect as of the balance sheet date of the amount of future tax deductions arising from all unused tax credit carryforwards which have been reduced by a valuation allowance. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition 
          Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from compensation and benefits costs. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition 
          Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from share-based compensation. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition 
          Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from accrued liabilities. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition 
          Amount of deferred tax liability attributable to taxable temporary differences net of deferred tax asset attributable to deductible temporary differences and carryforwards after valuation allowances. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition 
          Amount of deferred tax liability attributable to taxable temporary differences from capitalized software. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition 
          Amount of deferred tax liability attributable to taxable temporary differences from intangible assets including goodwill. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition 
          Amount of deferred tax liability attributable to taxable temporary differences not separately disclosed. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition 
          Amount of deferred tax liability attributable to taxable temporary differences from unrealized gains in other comprehensive income. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition 
          Amount of deferred tax liability attributable to taxable temporary differences from property, plant, and equipment. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition 
          Amount of deferred tax liability attributable to taxable temporary differences from tax deferred revenue or other income not separately disclosed. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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