Investments - Schedule of Marketable Securities in Unrealized Loss Position (Detail) $ in Millions	6 Months Ended
	Jul. 31, 2019 USD ($)
Debt Securities, Available-for-sale [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	$ 0
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	0
Marketable securities in an unrealized loss position for more than 12 months, Fair Value	205
Marketable securities in an unrealized loss position for more than 12 months, Unrealized Losses	(2)
Marketable securities in an unrealized loss position, Fair Value	205
Marketable securities in an unrealized loss position, Unrealized Losses	(2)
Unrealized losses on fixed rate investments, upper range value	1
Corporate notes and obligations
Debt Securities, Available-for-sale [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	0
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	0
Marketable securities in an unrealized loss position for more than 12 months, Fair Value	158
Marketable securities in an unrealized loss position for more than 12 months, Unrealized Losses	(1)
Marketable securities in an unrealized loss position, Fair Value	158
Marketable securities in an unrealized loss position, Unrealized Losses	(1)
U.S. treasury securities
Debt Securities, Available-for-sale [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	0
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	0
Marketable securities in an unrealized loss position for more than 12 months, Fair Value	47
Marketable securities in an unrealized loss position for more than 12 months, Unrealized Losses	(1)
Marketable securities in an unrealized loss position, Fair Value	47
Marketable securities in an unrealized loss position, Unrealized Losses	$ (1)