Summary of Business and Significant Accounting Policies (Policies)	9 Months Ended
	Jan. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation and Principles of Consolidation The Company prepares its unaudited condensed consolidated financial statements in accordance with generally accepted accounting principles in the United States, or GAAP, and applicable rules and regulations of the U.S. Securities and Exchange Commission (the “SEC”) regarding interim financial reporting. Accordingly, they do not include all disclosures normally required in annual consolidated financial statements prepared in accordance with GAAP. Therefore, these unaudited condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements and notes included in the Company’s final prospectus dated December 8, 2020, and filed with the SEC pursuant to Rule 424(b)(4) on December 9, 2020 (the “Final Prospectus”). In management’s opinion, these unaudited condensed consolidated financial statements have been prepared on the same basis as the annual financial statements and reflect all adjustments, which include only normal recurring adjustments necessary for the fair statement of the Company’s financial position as of January 31, 2021, and the results of operations for the three and nine months ended January 31, 2021. The results of operations for the three and nine months ended January 31, 2021, are not necessarily indicative of the results to be expected for the full year or any other future interim or annual period.
Principles of Consolidation	The condensed consolidated financial statements include the accounts of C3.ai, Inc. and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of the accompanying unaudited condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions about future events. These estimates and the underlying assumptions affect the amounts of assets and liabilities reported, disclosures about contingent assets and liabilities, and reported amounts of revenue and expenses. Actual results and outcomes could differ significantly from the Company’s estimates, judgments, and assumptions. Significant estimates include determining standalone selling price for performance obligations in contracts with customers and estimating variable consideration, the estimated expected benefit period for deferred contract acquisition costs, the useful lives of long-lived assets, the value of common stock and other assumptions used to measure stock-based compensation, and the valuation of deferred income tax assets and uncertain tax positions. These estimates and assumptions are based on management’s best estimates and judgment. Management evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors, including the current economic environment, which management believes to be reasonable under the circumstances. The Company adjusts such estimates and assumptions when facts and circumstances dictate. Changes in those estimates resulting from continuing changes in the economic environment will be reflected in the financial statements in future periods. As future events and their effects cannot be determined with precision, actual results could materially differ from those estimates and assumptions.
Fiscal Year	Fiscal YearThe Company’s fiscal year ends on April 30.
Concentration of Risk	Concentration of Risk Financial instruments that potentially subject the Company to concentration of credit risk consist of cash and cash equivalents, investments and accounts receivable. The majority of the Company’s cash and cash equivalents are held by one financial institution. The Company is exposed to that financial institution to the extent that its cash balance with that financial institution is in excess of Federal Deposit Insurance Company, or FDIC, insurance limits. The Company’s investment policy is to invest in securities with a minimum rating of P1 by Moody’s, A1 by Standard & Poor’s, F-1 by Fitch’s or higher for short-term investments, and minimum rating of A2 by Moody’s, A by Standard & Poor’s, or A by Fitch’s or higher for long-term investments.
Recent Accounting Pronouncements	Recent Accounting Pronouncements The Company currently qualifies as an “emerging growth company” under the Jumpstart Our Business Startups Act of 2012, or the JOBS Act. Accordingly, the Company is provided the option to adopt new or revised accounting guidance either (1) within the same periods as those otherwise applicable to public business entities or (2) within the same time periods as private companies, including early adoption when permissible. The Company has elected to adopt new or revised accounting guidance within the same time period as private companies. Other than policies noted below, there have been no significant changes to the accounting policies disclosed in Note 1 of the audited consolidated financial statements as of and for the years ended April 30, 2020 and 2019 included in the Final Prospectus. Recently Adopted Accounting Standards—In June 2016, the FASB issued ASU 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, which requires a financial asset measured at amortized cost basis to be presented at the net amount expected to be collected. Credit losses relating to available-for-sale debt securities should be recorded through an allowance for credit losses. The guidance also limits the amount of credit losses to be recognized for available-for-sale debt securities to the amount by which carrying value exceeds fair value and requires the reversal of previously recognized credit losses if fair value increases. The guidance is effective for the fiscal year beginning May 1, 2023 with early adoption permitted. The Company early adopted the guidance as of May 1, 2020 using a prospective transition method. Adoption of this guidance did not have a material impact to the Company’s consolidated financial statements and related disclosures. In January 2017, the FASB issued ASU No. 2017-04, Intangibles—Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment. ASU 2018-04 simplifies how an entity is required to test goodwill for impairment by eliminating Step 2 from the goodwill impairment test. The guidance is effective for the fiscal year beginning May 1, 2023 with early adoption permitted. The Company early adopted the guidance as of May 1, 2020 using a prospective transition method. Adoption of this guidance did not have a material impact to the Company’s consolidated financial statements and related disclosures. In July 2017, the FASB issued ASU No. 2017-11, Earnings Per Share (Topic 260), Distinguishing Liabilities from Equity (Topic 480), Derivatives and Hedging (Topic 815) I. Accounting for Certain Financial Instruments with Down Round Features II. Replacement of the Indefinite Deferral for Mandatorily Redeemable Financial Instruments of Certain Nonpublic Entities and Certain Mandatorily Redeemable Noncontrolling Interests with a Scope Exception. Part I of this standard applies to entities that issue financial instruments such as warrants, convertible debt or redeemable convertible preferred stock that contain down-round features. Part II of this standard replaces the indefinite deferral for certain mandatorily redeemable noncontrolling interests and mandatorily redeemable financial instruments of nonpublic entities contained within ASC Topic 480 with a scope exception and does not impact the accounting for these mandatorily redeemable instruments. The Company adopted the guidance as of May 1, 2020 using a prospective transition method. Adoption of this guidance did not have a material impact to the Company’s consolidated financial statements and related disclosures. In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement, which modifies the disclosure requirements on fair value measurements with respect to Level 3 rollforwards, timing of liquidation of investments in certain entities that calculate net asset value, and measurement uncertainty. The Company adopted the guidance as of May 1, 2020 using a prospective transition method. Adoption of this guidance did not have a material impact to the Company’s consolidated financial statements and related disclosures. Recently Issued Accounting Standards Not Yet Adopted—In August 2018, the FASB issued ASU 2018-15, Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement that is a Service Contract, which requires a customer in a cloud computing arrangement that is a service contract to follow the internal-use software guidance in ASC 350-40 to determine which implementation costs to defer and recognize as an asset. The guidance is effective for the fiscal year beginning May 1, 2021. Early adoption is permitted. The Company is currently evaluating the effect that this guidance will have on the consolidated financial statements and related disclosures.