Leases - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jul. 31, 2020	Jul. 31, 2019	Jul. 31, 2020	Jul. 31, 2019
Leases [Line Items]
Operating lease expense	$ 3	$ 2	$ 6	$ 3
Maximum
Leases [Line Items]
Operating leases, options to extend leases term	9 years		9 years
Finance leases, options to extend leases term	9 years		9 years