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Risk Management and Derivatives - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
 6 Months Ended
Nov. 30, 2012
Derivative Instruments and Hedging Activities Disclosure [Line Items]  
Total notional amount of outstanding derivatives $ 8,000
Percentage of anticipated exposures hedged (percent) 100.00%
Deferred net gains (net of tax) on both outstanding and matured derivatives accumulated in other comprehensive income are expected to be reclassified to net income during the next twelve months as a result of underlying hedged transactions also being recorded in net income 36
Maximum term over which the Company is hedging exposures to the variability of cash flows for its forecasted and recorded transactions (in months) 30 months
Aggregate fair value of derivative instruments with credit risk related contingent features that are in a net liability position 33
Embedded derivatives
  
Derivative Instruments and Hedging Activities Disclosure [Line Items]  
Notional amount of embedded derivatives 129
Minimum
  
Derivative Instruments and Hedging Activities Disclosure [Line Items]  
Typical time period that anticipated exposures are hedged against (in months) 12 months
Minimum fair value of outstanding derivative above which the credit related contingent features require the derivative party to post collateral $ 50
Maximum
  
Derivative Instruments and Hedging Activities Disclosure [Line Items]  
Typical time period that anticipated exposures are hedged against (in months) 18 months