Investments - Schedule of Marketable Securities in Unrealized Loss Position (Details) $ in Millions	9 Months Ended
	Oct. 31, 2020 USD ($)
Debt Securities, Available-for-sale [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	$ 966
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(4)
Marketable securities in an unrealized loss position for more than 12 months, Fair Value	0
Marketable securities in an unrealized loss position for more than 12 months, Unrealized Losses	0
Marketable securities in an unrealized loss position, Fair Value	966
Marketable securities in an unrealized loss position, Unrealized Losses	(4)
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	647
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(2)
Marketable securities in an unrealized loss position for more than 12 months, Fair Value	0
Marketable securities in an unrealized loss position for more than 12 months, Unrealized Losses	0
Marketable securities in an unrealized loss position, Fair Value	647
Marketable securities in an unrealized loss position, Unrealized Losses	(2)
Mortgage backed obligations
Debt Securities, Available-for-sale [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	151
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(1)
Marketable securities in an unrealized loss position for more than 12 months, Fair Value	0
Marketable securities in an unrealized loss position for more than 12 months, Unrealized Losses	0
Marketable securities in an unrealized loss position, Fair Value	151
Marketable securities in an unrealized loss position, Unrealized Losses	(1)
Asset backed securities
Debt Securities, Available-for-sale [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	168
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(1)
Marketable securities in an unrealized loss position for more than 12 months, Fair Value	0
Marketable securities in an unrealized loss position for more than 12 months, Unrealized Losses	0
Marketable securities in an unrealized loss position, Fair Value	168
Marketable securities in an unrealized loss position, Unrealized Losses	$ (1)