Employee and Director Stock Plans - Narrative (Detail) $ / shares in Units, $ in Millions		12 Months Ended			97 Months Ended
	Mar. 12, 2015 shares	Jan. 31, 2020 USD ($) period Plan $ / shares shares	Jan. 31, 2019 USD ($) $ / shares shares	Jan. 31, 2018 USD ($) $ / shares	Jan. 31, 2020 USD ($) 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
Grants in period, net of forfeitures (in shares)		0
Shares available for future issuance (in shares)		21,900,000			21,900,000
Options outstanding (in shares)		400,000	800,000		400,000
Non-vested stock options compensation cost not yet recognized | $		$ 30.4			$ 30.4
Restricted stock granted (in shares)		300,000
Liability classified awards, settled | $		$ 23.5
Market capitalization level of peer group | $		$ 2,000.0			$ 2,000.0
Number of exercise periods | period		4
Term of exercise period		6 months
Term of offering period		24 months
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
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)		13,800,000			13,800,000
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
Shares granted to shares issued (in shares)		2.11
Shares available for future issuance (in shares)		800,000			800,000
Reduction of shares reserved for issuance (in shares)	900,000
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]
Vesting period		4 years
Share based payment award options expiration term (in years)		10 years
Options outstanding (in shares)		300,000			300,000
BuildingConnected 2012 Plan
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Vesting period		4 years
Share based payment award options expiration term (in years)		10 years
Options outstanding (in shares)		100,000			100,000
ESP Plan
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Shares available for future issuance (in shares)		7,300,000			7,300,000
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 periods | 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 | $		$ 33.3	$ 27.2	$ 25.7
Stock Options and Restricted Stock | Employee Stock Plan 2012
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Grants in period, net of forfeitures (in shares)		50,600,000
Vesting period		3 years
Share based payment award options expiration term (in years)		10 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		$ 156.24	$ 144.37	$ 106.55
Fair value of units vested in period | $		$ 361.0	$ 425.4	$ 399.7
Restricted stock granted (in shares)		3,136,100
Number of awards granted but unreleased		4,732,300	4,287,400		4,732,300
Restricted Stock Units (RSUs)
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Total compensation cost related to non-vested awards not yet recognized, weighted average period of recognition (in years)		1 year 10 months 24 days
Restricted stock granted (in shares)		2,600,000
Share based compensation expense, restricted stock units | $		$ 274.5	$ 189.3	202.1
Total compensation cost related to non-vested awards not yet recognized | $		$ 474.6			$ 474.6
Number of awards granted but unreleased		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) | Directors stock plan 2012
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Grants in period, net of forfeitures (in shares)		900,000
Stock Option Plans
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Total compensation cost related to non-vested awards not yet recognized, weighted average period of recognition (in years)		2 years
Performance Stock Unit
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Vesting period		3 years
Total compensation cost related to non-vested awards not yet recognized, weighted average period of recognition (in years)		8 months 12 days
Restricted stock granted (in shares)		300,000
Share based compensation expense, restricted stock units | $		$ 27.1	$ 28.6	$ 33.7
Total compensation cost related to non-vested awards not yet recognized | $		$ 6.7			$ 6.7
Number of awards granted but unreleased		600,000			600,000
Performance Stock Unit | Year One
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Vesting percentage (up to percentage)		33.33%
Performance Stock Unit | Year Two
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Vesting percentage (up to percentage)		33.33%
Performance Stock Unit | Year Three
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Vesting percentage (up to percentage)		33.33%