Investments - Maturity (Details) $ in Millions	Jul. 31, 2020 USD ($)
Cost Basis
Due in one year or less	$ 433
Due after one year through five years	319
Total	752
Fair Value
Due in one year or less	435
Due after one year through five years	326
Total	761
Held-to-Maturity
Due in one year or less	650
Due after one year through five years	0
Total	$ 650