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Fair Value Measurements and Investments - Investment Income (Detail) - USD ($) $ in Millions | 12 Months Ended
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Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2021
Fair Value Disclosures [Abstract] |  |  |
Interest and dividend income on cash and investments | $ 745 | $ 69 | $ (16)
Equity securities: |  |  |
Unrealized gains (losses), net | (84) | (364) | 721
Realized gains (losses), net | 2 | 68 | 26
Investment income (expense) | $ 663 | $ (227) | $ 731

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- Definition Amount of operating dividend and interest income, including amortization and accretion of premiums and discounts, on securities. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 946 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.6-07(1)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 946 -SubTopic 320 -Name Accounting Standards Codification -Section S99 -Paragraph 6 -Subparagraph (SX 210.12-14(Column E)(Footnote 4)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480032/946-320-S99-6 + Details
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