Employee and Director Stock Plans - Stock-Based Compensation Expense - Additional Information (Detail) $ / shares in Units, $ in Millions		12 Months Ended			73 Months Ended
	Mar. 12, 2015 shares	Jan. 31, 2018 USD ($) period Plan $ / shares shares	Jan. 31, 2017 USD ($) $ / shares shares	Jan. 31, 2016 USD ($) $ / shares	Jan. 31, 2018 shares
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Number of active stock plans | Plan		2
Number of additional share authorized (in shares)					36,100,000
Shares available for future issuance (in shares)		31,300,000			31,300,000
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)		21,300,000			21,300,000
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)		900,000			900,000
Reduction of shares reserved for issuance (in shares)	900,000
Outside directors stock plan 2012 | Minimum
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Vesting period		1 year
Outside directors stock plan 2012 | Maximum
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Vesting period		3 years
ESP Plan
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Shares available for future issuance (in shares)		9,100,000			9,100,000
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 | $		$ 25.7	$ 25.9	$ 27.1
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)		41,100,000
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		$ 106.55	$ 65.95	$ 52.53
Fair value of units vested in period | $		$ 399.7	$ 232.2	$ 193.3
Restricted stock granted (in shares)		2,481,800
Number of awards granted but unreleased		5,670,700	7,622,400		5,670,700
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 | $		$ 202.1	$ 173.0	146.4
Total compensation cost related to non-vested awards not yet recognized | $		$ 310.2
Total compensation cost related to non-vested awards not yet recognized, weighted average period of recognition (in years)		1 year 7 months 24 days
Number of awards granted but unreleased		5,100,000			5,100,000
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
Performance Stock Units (PSUs)
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 | $		$ 33.7	$ 22.9	$ 23.2
Total compensation cost related to non-vested awards not yet recognized | $		$ 6.8
Total compensation cost related to non-vested awards not yet recognized, weighted average period of recognition (in years)		9 months 3 days
Number of awards granted but unreleased		600,000			600,000
Performance Stock Units (PSUs) | Year One
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Vesting percentage (up to percentage)		33.33%
Performance Stock Units (PSUs) | Year Two
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Vesting percentage (up to percentage)		33.33%
Performance Stock Units (PSUs) | Year Three
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Vesting percentage (up to percentage)		33.33%
Chief Executive Officer | Performance Stock Units (PSUs)
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Accelerated stock based compensation costs | $		$ 7.3