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Fair Value Measurements - Summary of Investment Income, Net Gains and Losses, Funds restricted for Specific Transactions and Disbursements Related to Investments (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Mar. 31, 2025 | Mar. 31, 2024 | Mar. 31, 2025 | Mar. 31, 2024
Fair Value Disclosures [Abstract] |  |  |  |  |
Investment income | [1] | $ 3 | $ 3 | $ 8 | $ 9
Net gains (losses) | [1] | 3 | 9 | (14) | 39
Funds restricted for specific transactions |  | 8 | 0 | 8 | 5
Disbursements |  | $ (19) | $ (21) | $ (25) | $ (37)
[1] | Included in the net interest and other expense (income) caption within the Statements of Condensed Consolidated Comprehensive Income (Loss).

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- Definition Amount of unrealized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(3)(d)(2)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477250/944-220-S99-1 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 321 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 4 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479536/321-10-50-4 + Details
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