Employee and Director Stock Plans - Summary of Restricted Stock Activity (Detail) - $ / shares	12 Months Ended
	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2017
Restricted Stock Units (RSUs) and Performance Stock Units (PSUs)
Unreleased Restricted Stock Units (in thousands)
Unvested restricted stock, beginning balance (in shares)	5,670,700
Granted (in shares)	2,250,700
Vested (in shares)	(2,982,000.0)
Canceled/Forfeited (in shares)	(681,900)
Performance Adjustment (in shares)	29,900
Unvested restricted stock, ending balance (in shares)	4,287,400	5,670,700
Weighted average grant date fair value per share
Unvested restricted stock, beginning balance (in dollars per share)	$ 82.94
Granted (in dollars per share)	144.37	$ 106.55	$ 65.95
Vested (in dollars per share)	76.30
Canceled/Forfeited (in dollars per share)	94.70
Performance Adjustment (in dollars per share)	101.74
Unvested restricted stock, ending balance (in dollars per share)	$ 120.07	$ 82.94
Performance Stock Unit
Unreleased Restricted Stock Units (in thousands)
Granted (in shares)	200,000
Unvested restricted stock, ending balance (in shares)	400,000
Minimum | Performance Stock Unit
Weighted average grant date fair value per share
Performance shares payout		90.00%
Maximum | Performance Stock Unit
Weighted average grant date fair value per share
Performance shares payout		117.60%