Debt - Schedule of Interest Expense (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jul. 31, 2020	Jul. 31, 2019	Jul. 31, 2020	Jul. 31, 2019
Debt Disclosure [Abstract]
Contractual interest expense	$ 24	$ 28	$ 48	$ 56
Amortization of debt issuance costs	1	1	2	2
Debt interest expense	$ 25	$ 29	$ 50	$ 58