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Derivative Instruments (Detail) - Forward Contracts - USD ($)
$ in Millions
3 Months Ended
Apr. 30, 2019
Jan. 31, 2019
Not Designated as Hedging Instrument    
Derivative [Line Items]    
Derivative, notional amount $ 134 $ 198
Cash Flow Hedging | Designated as Hedging Instrument    
Derivative [Line Items]    
Derivative, notional amount $ 788 $ 717
Cash Flow Hedging | Designated as Hedging Instrument | Maximum    
Derivative [Line Items]    
Derivative, remaining maturity 36 months