Investments - Schedule of Short-Term and Long-Term Marketable Securities (Detail) - USD ($) $ in Millions	Apr. 30, 2018	Jan. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Due within 1 year	$ 202	$ 395
Due in 1 year through 5 years	1,031	1,579
Due in 5 years through 10 years	4	4
Fair Value of Marketable Securities	$ 1,237	$ 1,978