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Related Party Transactions (Detail) - USD ($)
$ in Millions
1 Months Ended 3 Months Ended
Jan. 31, 2014
Apr. 30, 2018
Apr. 30, 2017
Related Party Transaction [Line Items]      
Term of agreements (in years) 95 years    
Chairman, Mr. Duffield      
Related Party Transaction [Line Items]      
Term of agreements (in years)   9 years  
Rent expense   $ 3 $ 2