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Income Tax - Additional Information (Detail) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Jun. 30, 2026 | Jun. 30, 2025 | Jun. 30, 2026 | Jun. 30, 2025
Income Taxes [Line Items] |  |  |  |
Net discrete tax expense (benefit) | $ 19 | $ 1 | $ 30 | $ 10
United States Internal Revenue Service (IRS) [Member] |  |  |  |
Income Taxes [Line Items] |  |  |  |
Tax years remain subject to examination |  |  | 2023 2024 2025 |
State Tax Authorities [Member] |  |  |  |
Income Taxes [Line Items] |  |  |  |
Tax years remain subject to examination |  |  | 2019 2020 2021 2022 2023 2024 2025 |
Foreign Jurisdictions [Member] |  |  |  |
Income Taxes [Line Items] |  |  |  |
Tax years remain subject to examination |  |  | 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 |

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- Definition Tax year that remains open to examination under enacted tax laws, in YYYY format. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 15 -Subparagraph (e) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482685/740-10-50-15 + Details
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