Derivative Instruments (Detail) - Forward Contracts - USD ($) $ in Millions |
3 Months Ended | |
|---|---|---|
Apr. 30, 2017 |
Jan. 31, 2017 |
|
| Designated as Hedging Instrument | ||
| Derivative [Line Items] | ||
| Derivative, notional amount | $ 325 | $ 252 |
| Designated as Hedging Instrument | Maximum | ||
| Derivative [Line Items] | ||
| Derivative, remaining maturity | 25 months | |
| Not Designated as Hedging Instrument | ||
| Derivative [Line Items] | ||
| Derivative, notional amount | $ 42 | $ 51 |
| Not Designated as Hedging Instrument | Maximum | ||
| Derivative [Line Items] | ||
| Derivative, remaining maturity | 15 months |