Commitment and Contingencies (Details) - USD ($)	1 Months Ended		12 Months Ended
	Feb. 29, 2020	Nov. 30, 2019	Apr. 30, 2021	Apr. 30, 2020	Apr. 30, 2019
Long-term Purchase Commitment [Line Items]
Purchase commitment, incurred cost			$ 14,300,000	$ 4,400,000	$ 3,400,000
Blattman et al. v. Siebel et al. | Pending Litigation
Long-term Purchase Commitment [Line Items]
Loss contingency, damages sought	$ 2,500,000
C3.ai DTI Grants Program
Long-term Purchase Commitment [Line Items]
Grants, payment period	5 years
Grants, potential remaining contributions			$ 43,100,000	$ 45,800,000
Web-Hosting Services, November 2019-November 2022
Long-term Purchase Commitment [Line Items]
Purchase commitment		$ 30,000,000.0
Purchase commitment, term		3 years
Web-Hosting Services, November 2020
Long-term Purchase Commitment [Line Items]
Purchase commitment		$ 10,000,000.0
Web-Hosting Services, November 2021
Long-term Purchase Commitment [Line Items]
Purchase commitment		10,000,000.0
Web-Hosting Services, November 2022
Long-term Purchase Commitment [Line Items]
Purchase commitment		$ 10,000,000.0