Description of Organization and Business Operations	9 Months Ended
Description of Organization and Business Operations	Sep. 30, 2021
Description of Organization and Business Operations [Abstract]
Description of Organization and Business Operations	Description of Organization and Business Operations On October 1, 2020, our predecessor company, Tortoise Acquisition Corp. (“Tortoise”), consummated a business combination (the “Business Combination”) with Hyliion Inc., a Delaware corporation (“Legacy Hyliion”) pursuant to which Legacy Hyliion merged with and into SHLL Merger Sub, Inc., a Delaware corporation and a wholly-owned subsidiary of Tortoise, with Legacy Hyliion surviving the merger (together with the related transactions, the “Business Combination”). Upon consummation of the Business Combination, Legacy Hyliion became a direct wholly-owned subsidiary of Tortoise, and Tortoise was renamed Hyliion Holdings Corp. References to the “Company” in this report refer to Tortoise before the consummation of the Business Combination or Hyliion Holdings Corp. and its wholly-owned subsidiary (“Hyliion”, “we” or “us”) after the Business Combination, unless expressly indicated or the context otherwise requires. Hyliion designs and develops hybrid and electrified powertrain systems for long haul “Class 8” semi-trucks which modify semi-tractors into hybrid and fully electric range extender vehicles, respectively. The Company’s hybrid powertrain system "Hybrid eX" utilizes intelligent electric drive axles with advanced algorithms and battery technology to optimize fuel savings and vehicle performance with reduced emissions, enabling fleets to access an easy, efficient way to decrease fuel expenses, lower emissions and/or improve vehicle performance. The Company’s fully electric range extender systems utilize an intelligent electric powertrain with advanced algorithms to optimize emissions performance and efficiency with no new infrastructure required. The Hypertruck ERX system enables fleets to reduce the cost of ownership while providing the ability to deliver net-negative carbon emissions and operate fully electric when needed. The Company recently launched its commercial Hybrid eX and the Hypertruck ERX system is in the prototype phase. On October 1, 2020, the Company consummated a business combination which was accounted for as a reverse recapitalization. For more details on the reverse recapitalization, see Note 3 to the Company's Consolidated Financial Statements as presented in its Annual Report, as amended on Form 10-K/A for the year ended December 31, 2020. As a result of the reverse recapitalization, all references to numbers of common shares and per common share data for 2020 in these condensed consolidated financial statements and related notes have been retroactively adjusted to account for the effect of the reverse recapitalization. These condensed consolidated financial statements have been prepared on a going concern basis, which contemplates the realization of assets and settlement of liabilities in the normal course of business. The Company is an early-stage growth company in the pre-commercialization stage of development and has generated negative cash flows from operating activities since inception. As of September 30, 2021, the Company had a cash and cash equivalents balance of $289.5 million and total investments of $299.4 million. Based on this, the Company has sufficient funds to continue to execute its business strategy for the next twelve months.