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Derivative Instruments (Detail) - Forward Contracts - USD ($)
$ in Millions
9 Months Ended
Oct. 31, 2018
Jan. 31, 2018
Designated as Hedging Instrument    
Derivative [Line Items]    
Derivative, notional amount $ 711 $ 549
Designated as Hedging Instrument | Maximum    
Derivative [Line Items]    
Derivative, remaining maturity 36 months  
Not Designated as Hedging Instrument    
Derivative [Line Items]    
Derivative, notional amount $ 213 $ 75