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Related Party Transactions (Details) - USD ($) | 1 Months Ended | 3 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | ---
Oct. 31, 2025 | Feb. 28, 2023 | Jun. 30, 2026 | Jun. 30, 2025 | Mar. 31, 2026 | Mar. 31, 2025 | Mar. 31, 2022
Related Party Transaction [Line Items] |  |  |  |  |  |  |
Revenue |  |  | $ 1,289,000,000 | $ 1,053,000,000 |  |  |
Operating expenses |  |  | 1,162,000,000 | 909,000,000 |  |  |
Other current liabilities |  |  | 696,000,000 |  | $ 447,000,000 |  |
Contract liabilities current |  |  | 200,000,000 |  | 294,000,000 |  |
Contract liabilities noncurrent |  |  | 739,000,000 |  | 752,000,000 |  |
Additional (reversal of) provision |  |  | 0 | (1,000,000) |  |  |
Accounts receivable, allowance |  |  | 31,000,000 | 19,000,000 | 31,000,000 | $ 20,000,000 |
Contract asset, current |  |  | 881,000,000 |  | 977,000,000 |  |
Contract asset, noncurrent |  |  | 366,000,000 |  | 320,000,000 |  |
Accounts receivable, net |  |  | 1,119,000,000 |  | 1,300,000,000 |  |
Proceeds from equity method investments |  |  | 800,000 | 1,800,000 |  |  |
Related Party |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |
Revenue |  |  | 388,000,000 | 328,000,000 |  |  |
Operating lease, lease income, lease payments |  |  | 300,000 | 200,000 |  |  |
Other current liabilities |  |  | 30,000,000 |  | 20,000,000 |  |
Contract liabilities current |  |  | 29,000,000 |  | 36,000,000 |  |
Contract liabilities noncurrent |  |  | 23,000,000 |  | 23,000,000 |  |
Contract asset, current |  |  | 577,000,000 |  | 646,000,000 |  |
Accounts receivable, net |  |  | 281,000,000 |  | 270,000,000 |  |
Related Party | Arduino |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |
Loan receivable, noncurrent |  |  |  |  |  | $ 16,600,000 |
Proceeds from settlement of loans, including convertible loans | $ 16,900,000 |  |  |  |  |  |
Loan receivable, credit loss reversal |  |  |  |  | 16,800,000 |  |
Related Party | Cerfe Labs, Inc. | Loans receivable |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |
Loans receivable, gross, noncurrent |  |  | 3,200,000 |  | 3,200,000 |  |
IP Licensing Revenue | Related Party |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |
Revenue |  |  | 189,400,000 | 201,000,000.0 |  |  |
Net receivable |  |  | 283,500,000 |  | 276,200,000 |  |
Accounts receivable, before allowance for credit loss, current |  |  | 308,300,000 |  | 296,500,000 |  |
Other current liabilities |  |  | 24,800,000 |  | 20,300,000 |  |
Contract liabilities current |  |  | 29,000,000.0 |  | 30,300,000 |  |
Contract liabilities noncurrent |  |  | 23,300,000 |  | 23,300,000 |  |
Additional (reversal of) provision |  |  | 0 | 0 |  |  |
Accounts receivable, allowance |  |  | 28,300,000 |  | 28,300,000 |  |
Service Share Arrangement | Related Party |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |
Operating expenses |  |  | 17,200,000 | 13,900,000 |  |  |
Contract termination costs |  |  | 6,800,000 |  |  |  |
Common Control in SoftBank | Related Party |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |
Revenue |  |  | 192,900,000 | 126,100,000 |  |  |
Contract asset, current |  |  | 576,100,000 |  | 645,800,000 |  |
Contract asset, noncurrent |  |  | 1,100,000 |  | 0 |  |
Common Control in SoftBank | Related Party | Ampere |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |
Revenue |  |  | 5,400,000 | 600,000 |  |  |
Other Equity Investments | Related Party |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |
Contract liabilities current |  |  | 400,000 |  | 5,400,000 |  |
Contract asset, current |  |  | 500,000 |  | 500,000 |  |
Operating costs and expenses |  |  | 5,000,000.0 |  |  |  |
Prepaid expense |  |  | 5,000,000.0 |  |  |  |
Accounts payable |  |  | 5,000,000.0 |  |  |  |
Accounts receivable, net |  |  | $ 0 |  | $ 500,000 |  |
Linaro Agreement | Related Party |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |
Subscription costs incurred |  |  |  | $ 2,300,000 |  |  |
Amounts of transaction |  | $ 4,000,000.0 |  |  |  |  |
Related party transaction, term |  | 5 years |  |  |  |  |
Acetone Limited |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |
Ownership percentage |  |  |  |  |  |  | 10.00%
Arm China | Acetone Limited |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |
Ownership percentage |  |  |  |  |  |  | 48.20%

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