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Long-term Debt and Fair Value Disclosure (Details) - USD ($)
Oct. 31, 2015
Apr. 30, 2015
Debt Instrument    
Fair value of long-term debt $ 877,000,000 $ 887,000,000
Line of Credit    
Debt Instrument    
Maximum borrowing capacity 100,000,000 100,000,000
Fair value of amount outstanding $ 0 $ 0