Document and Entity Information - USD ($) $ in Billions	12 Months Ended
	Apr. 30, 2021	Jun. 18, 2021
Document Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Apr. 30, 2021
Current Fiscal Year End Date	--04-30
Document Transition Report	false
Entity File Number	001-39744
Entity Registrant Name	C3.ai, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	26-3999357
Entity Address, Address Line One	1300 Seaport Blvd,
Entity Address, Address Line Two	Suite 500
Entity Address, City or Town	Redwood City,
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94063
City Area Code	650
Local Phone Number	503-2200
Title of 12(b) Security	Class A Common Stock, par value $0.001 per share
Trading Symbol	AI
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
ICFR Auditor Attestation Flag	false
Entity Shell Company	false
Entity Public Float	$ 4.3
Documents Incorporated by Reference	Portions of the registrant’s definitive proxy statement relating to its 2021 annual meeting of shareholders (the “2021 Proxy Statement”) are incorporated by reference into Part III of this Annual Report on Form 10-K where indicated. The 2021 Proxy Statement will be filed with the U.S. Securities and Exchange Commission within 120 days after the end of the registrant’s fiscal year ended April 30, 2021.
Amendment Flag	false
Entity Central Index Key	0001577526
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Class A Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding (in shares)		99,920,942
Class B Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding (in shares)		3,499,992