Fair Value Measurements and Investments - Continuous Unrealized Losses for Less than 12 Months and More than 12 Months (Details) - USD ($) $ in Millions |
Sep. 30, 2023 |
Sep. 30, 2022 |
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| Debt Securities, Available-for-sale [Line Items] | ||
| Less Than 12 Months, Fair Value | $ 1,772 | $ 3,915 |
| Less Than 12 Months, Gross Unrealized Losses | (14) | (134) |
| 12 Months or Greater, Fair Value | 2,178 | |
| 12 Months or Greater, Gross Unrealized Losses | (68) | |
| U.S. government-sponsored debt securities | ||
| Debt Securities, Available-for-sale [Line Items] | ||
| Less Than 12 Months, Fair Value | 412 | 408 |
| Less Than 12 Months, Gross Unrealized Losses | (2) | (1) |
| 12 Months or Greater, Fair Value | 50 | |
| 12 Months or Greater, Gross Unrealized Losses | 0 | |
| U.S. Treasury securities | ||
| Debt Securities, Available-for-sale [Line Items] | ||
| Less Than 12 Months, Fair Value | 1,360 | 3,507 |
| Less Than 12 Months, Gross Unrealized Losses | (12) | $ (133) |
| 12 Months or Greater, Fair Value | 2,128 | |
| 12 Months or Greater, Gross Unrealized Losses | $ (68) |
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- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- Definition Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset. Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
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- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- Definition Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset. Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
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- Definition 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. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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