Investments - Schedule of Components of Investment Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Oct. 31, 2020	Oct. 31, 2019	Oct. 31, 2020	Oct. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Interest income	$ 17	$ 32	$ 63	$ 89
Realized gains	4	0	6	1
Realized losses	(2)	0	(3)	(1)
Investment income	$ 19	$ 32	$ 66	$ 89