Employee Incentive Plans - Schedule of Restricted Stock Unit Activity (Details) - Restricted stock units	6 Months Ended
	Jul. 31, 2018 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning balance (in shares) | shares	2,862,929
Granted during period (in shares) | shares	2,752,588
Vested during period (in shares) | shares	(542,969)
Forfeited during period (in shares) | shares	(181,762)
Ending balance (in shares) | shares	4,890,786
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Beginning balance (in dollars per share) | $ / shares	$ 24.38
Granted during period (in dollars per share) | $ / shares	50.67
Vested during period (in dollars per share) | $ / shares	22.71
Forfeited during period (in dollars per share) | $ / shares	29.39
Ending balance (in dollars per share) | $ / shares	$ 39.17