Equity Compensation - Narrative (Details) $ / shares in Units, $ in Millions			3 Months Ended	12 Months Ended			104 Months Ended
	Nov. 23, 2020 shares	Mar. 12, 2015 shares	Jan. 31, 2021 USD ($) shares	Jan. 31, 2021 USD ($) period Plan $ / shares shares	Jan. 31, 2020 USD ($) $ / shares shares	Jan. 31, 2019 USD ($) $ / shares	Jan. 31, 2021 USD ($) shares	Jan. 29, 2021 shares
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Number of active stock plans | Plan				4
Number of additional share authorized (in shares)							36,100,000
Shares available for future issuance (in shares)			17,300,000	17,300,000			17,300,000
Liability classified awards, settled | $				$ 28.7	$ 23.5	$ 0.0
Market capitalization level of peer group | $			$ 2,000.0	2,000.0			$ 2,000.0
Stock-based compensation expense related to stock awards and Employee Qualified Stock Purchase Plan ("ESPP") purchases | $				$ 399.8	362.4	249.5
Number of exercise period | period				4
Term of exercise period				6 months
Term of offering period				24 months
Common Stock
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Liability classified awards, settled | $				$ 28.7	23.5
Spacemaker
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Vesting period	3 years
Shares issued in period (in shares)	73,632
Stock-based compensation expense related to stock awards and Employee Qualified Stock Purchase Plan ("ESPP") purchases | $			2.0
Restricted Stock Units (RSUs)
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Restricted stock granted (in shares)				2,200,000
Share based compensation expense, restricted stock units | $				$ 308.9	$ 274.5	$ 189.3
Total compensation cost related to non-vested awards not yet recognized | $			$ 617.7	$ 617.7			$ 617.7
Total compensation cost related to non-vested awards not yet recognized, weighted average period of recognition				1 year 9 months 18 days
Number of awards granted but unreleased			4,100,000	4,100,000			4,100,000
Restricted Stock Units (RSUs) | Maximum
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Vesting period				3 years
Restricted Stock Units (RSUs) and Performance Stock Units (PSUs)
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Granted (in dollars per share) | $ / shares				$ 224.20	$ 156.24	$ 144.37
Fair value of units vested in period | $				$ 503.4	$ 361.0	$ 425.4
Restricted stock granted (in shares)				2,462,200
Number of awards granted but unreleased			4,507,100	4,507,100	4,732,300		4,507,100
Performance Stock Unit
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Vesting period				3 years
Restricted stock granted (in shares)				300,000
Share based compensation expense, restricted stock units | $				$ 30.7	$ 27.1	28.6
Total compensation cost related to non-vested awards not yet recognized | $			$ 5.0	$ 5.0			$ 5.0
Total compensation cost related to non-vested awards not yet recognized, weighted average period of recognition				9 months 18 days
Number of awards granted but unreleased			400,000	400,000			400,000
Common Stock
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Stock-based compensation expense related to stock awards and Employee Qualified Stock Purchase Plan ("ESPP") purchases | $				$ 2.4
Common Stock | Spacemaker
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Shares of common stock reserved for issuance (in shares)								17,662
Value of shares authorized | $			$ 4.9	$ 4.9			$ 4.9
Restricted Stock | Spacemaker
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Vesting period				3 years
Shares issued in period (in shares)				73,632
Employee Stock Plan 2012
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Shares of common stock reserved for issuance (in shares)			57,300,000	57,300,000			57,300,000
Restricted stock award, net of forfeitures (in shares)				51,300,000
Shares forfeited (in shares)				6,000,000.0
Shares granted to shares issued (in shares)				1.79
Shares available for future issuance (in shares)			10,000,000.0	10,000,000.0			10,000,000.0
Employee Stock Plan 2012 | Stock Options and Restricted Stock
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Grants in period, net of forfeitures (in shares)				55,000,000.0
Share based payment award options expiration term (in years)				10 years
Vesting period				3 years
Directors stock plan 2012
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Shares of common stock reserved for issuance (in shares)			1,700,000	1,700,000			1,700,000
Shares granted to shares issued (in shares)				2.11
Shares available for future issuance (in shares)			800,000	800,000			800,000
Reduction of shares reserved for issuance (in shares)		900,000
Directors stock plan 2012 | Restricted Stock Units (RSUs)
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Grants in period, net of forfeitures (in shares)				1,000,000.0
2012 Outside Directors' Plan | Minimum
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Vesting period				1 year
2012 Outside Directors' Plan | Maximum
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Vesting period				3 years
PlanGrid 2012 Plan
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Share based payment award options expiration term (in years)				10 years
Vesting period				4 years
Options outstanding (in shares)			10,000	10,000			10,000
BuildingConnected 2012 Plan
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Share based payment award options expiration term (in years)				10 years
Vesting period				4 years
Options outstanding (in shares)			38,000	38,000			38,000
ESP Plan
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Shares available for future issuance (in shares)			6,400,000	6,400,000			6,400,000
Percentage of compensation that eligible employees can use to purchase common stock, maximum				15.00%
Percentage of fair market value eligible employees can purchase common stock, minimum				85.00%
Number of exercise period | period				4
Term of exercise period				6 months
Term of offering period				24 months
Employee service share based compensation recognized compensation costs on nonvested restricted shares | $				$ 40.1	$ 33.3	$ 27.2