Retirement Benefits - Schedule of Amounts Included in Accumulated Other Comprehensive Loss, Net of Tax (Details) - USD ($) $ in Millions |
Sep. 30, 2026 |
Sep. 30, 2025 |
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| Pension Benefits | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Prior service (credit) cost | $ (164) | $ (154) |
| Net actuarial loss | 255 | 475 |
| Total | 91 | 321 |
| Other Postretirement Benefits | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Prior service (credit) cost | 4 | 4 |
| Net actuarial loss | 11 | 10 |
| Total | $ 15 | $ 14 |
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- Definition Amount, after tax, of accumulated other comprehensive (income) loss for defined benefit plan, that has not been recognized in net periodic benefit cost (credit). Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Amount, after tax, of accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Amount, after tax, of accumulated other comprehensive (income) loss for cost (credit) of benefit change attributable to participants' prior service from plan amendment or plan initiation of defined benefit plan, that has not been recognized in net periodic benefit cost (credit). Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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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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