Equity Incentive Plans - Stock Options and Restricted Stock Units, Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Payment Arrangement, Nonvested Award, Excluding Option, Cost Not yet Recognized, Amount	$ 2.2
Weighted-average grant date fair value (in dollars per share)			$ 4.76
Options granted (in shares)	0
Intrinsic value	$ 293.9	$ 198.9	$ 4.1
Stock options vested, fair value	6.3	$ 15.9	$ 13.5
Share-based compensation cost not yet recognized	$ 5.1
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted (in shares)	0	0
Share-based compensation, period for recognition	1 year 2 months 12 days
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Payment Arrangement, Nonvested Award, Excluding Option, Cost Not yet Recognized, Amount	$ 310.2
Share-based compensation, period for recognition	3 years 1 month 6 days

Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Amount of cost to be recognized for nonvested award under share-based payment arrangement. Excludes share and unit options.

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Amount of cost to be recognized for option under share-based payment arrangement.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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Gross number of share options (or share units) granted during the period.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

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