Stock-Based Compensation - Schedule of Stock-based Compensation Expense Included in Respective Expense Category (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 85.6	$ 51.8	$ 156.0	$ 81.9
Location, Statement of Income, Balance [Axis]: us-gaap:ResearchAndDevelopmentExpense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	41.2	22.9	73.3	34.0
Location, Statement of Income, Balance [Axis]: achr:GeneralAndAdministrativeExpenseCredit
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 44.4	$ 28.9	$ 82.7	$ 47.9

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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+ Details