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Related Party Transactions (Detail) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Oct. 31, 2018
Oct. 31, 2017
Oct. 31, 2018
Oct. 31, 2017
Jan. 31, 2014
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) 8 years   8 years    
Rent expense $ 3 $ 2 $ 8 $ 6