Financial Statements	3 Months Ended
Financial Statements	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Financial Statements	Financial Statements The consolidated financial statements include the consolidated accounts of Johnson Controls International plc, a corporation organized under the laws of Ireland, and its subsidiaries (Johnson Controls International plc and all its subsidiaries, hereinafter collectively referred to as the "Company" or "Johnson Controls"). In the opinion of management, the accompanying unaudited consolidated financial statements contain all adjustments (which include normal recurring adjustments) necessary to state fairly the financial position, results of operations and cash flows for the periods presented. Certain information and footnote disclosures normally included in financial statements prepared in accordance with accounting principles generally accepted in the United States of America ("U.S. GAAP") have been omitted pursuant to the rules and regulations of the United States Securities and Exchange Commission ("SEC"). These consolidated financial statements should be read in conjunction with the audited financial statements and notes thereto included in the Company's Annual Report on Form 10-K for the year ended September 30, 2020 filed with the SEC on November 16, 2020. The results of operations for the three month period ended December 31, 2020 are not necessarily indicative of results for the Company’s 2021 fiscal year because of seasonal and other factors. Nature of Operations Johnson Controls International plc, headquartered in Cork, Ireland, is a global diversified technology and multi-industrial leader serving a wide range of customers in more than 150 countries. The Company’s products and solutions enable smart, energy efficient, sustainable buildings that work seamlessly together to advance the safety, comfort and intelligence of spaces to power its customers’ mission. The Company is committed to helping its customers win and creating greater value for all of its stakeholders through its strategic focus on buildings. The Company is a global leader in engineering, manufacturing and commissioning building products and systems, including residential and commercial heating, ventilating, air-conditioning ("HVAC") equipment, industrial refrigeration systems, controls, security systems, fire detection systems and fire suppression solutions. The Company further serves customers by providing technical services, including maintenance, repair, retrofit and replacement of equipment (in the HVAC, security and fire-protection space), energy-management consulting and data-driven “smart building” services and solutions powered by its digital platforms and capabilities. Principles of Consolidation The consolidated financial statements include the consolidated accounts of Johnson Controls International plc and its subsidiaries that are consolidated in conformity with U.S. GAAP. All significant intercompany transactions have been eliminated. The results of companies acquired or disposed of during the year are included in the consolidated financial statements from the effective date of acquisition or up to the date of disposal. Investments in partially-owned affiliates are accounted for by the equity method when the Company’s interest exceeds 20% and the Company does not have a controlling interest. The Company consolidates variable interest entities ("VIE") in which the Company has the power to direct the significant activities of the entity and the obligation to absorb losses or receive benefits from the entity that may be significant. The Company did not have a significant variable interest in any consolidated or nonconsolidated VIEs in its continuing operations for the presented reporting periods. Restricted Cash At December 31, 2020 and September 30, 2020, the Company held restricted cash of approximately $5 million and $9 million, respectively, all of which was recorded within other current assets in the consolidated statements of financial position. These amounts were related to cash restricted for payment of asbestos liabilities.