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Common Stock and Stockholders' Equity (Narrative) (Detail) $ / shares in Units, $ in Millions	1 Months Ended	12 Months Ended
	Mar. 31, 2017 shares	Jan. 31, 2019 USD ($) vote / shares $ / shares shares	Jan. 31, 2018 USD ($) $ / shares shares	Jan. 31, 2017 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option grants (in shares)		0	0	0
Employee Stock Purchase Plan (ESPP)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock available for future grants, shares		6,000,000
Percentage of fair market value of stock at which employees are granted shares		85.00%
Weighted average grant date fair value (in dollars per share) \| $ / shares		$ 96.12
Number of shares purchased by employees, shares		1,000,000
Cash proceeds \| $		$ 83
Class A Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock outstanding, shares		157,000,000	142,000,000
Common stock, votes per share \| vote / shares		1
Class A Common Stock \| 2012 Equity Incentive Plan (EIP)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share reserve increased, shares	11,000,000
Common stock available for future grants, shares		65,000,000
Class B Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock outstanding, shares		65,000,000	70,000,000
Common stock, votes per share \| vote / shares		10
Percent of shares of common stock less than 9% of the outstanding shares		9.00%
Duration of time after death of Co-Founders until shares are converted, months		9 months
Restricted Stock Units (RSU)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period, years		4 years
Weighted average grant date fair value (in dollars per share) \| $ / shares		$ 129.62	$ 88.90	$ 75.71
Total grant-date fair value of units vested \| $		$ 801	$ 528	$ 303
Unrecognized compensation cost \| $		$ 1,200
Weighted-average period to be recognized, years		2 years 8 months 12 days
Number of shares granted, (in shares)		6,991,459
Performance-based Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost \| $		$ 15
Weighted-average period to be recognized, years		2 months
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period, years		5 years
Weighted-average period to be recognized, years		2 years 3 months 18 days
Unrecognized compensation cost \| $		$ 72
Maximum exercise period, years		10 years
Fair value of options vested in period \| $		$ 29	5	14
Total intrinsic value of the options exercised \| $		$ 261	$ 234	$ 273
Weighted-average remaining contractual life of vested and expected to vest options, years		3 years 2 months 12 days
Weighted-average remaining contractual life of exercisable options, years		2 years 5 months 5 days
Weighted-average remaining contractual life of outstanding options, years		3 years 3 months 7 days
Weighted-average grant-date fair value of stock options assumed (usd per share) \| $ / shares		$ 100.69
Vesting March 15 2018 \| All Other Employees \| Performance-based Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted, (in shares)			400,000
Compensation cost \| $		$ 7
Vesting March 15 2019 \| All Other Employees \| Performance-based Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted, (in shares)		500,000
Compensation cost \| $		$ 51