Acquisitions and Divestitures - Summarized Results of Discontinued Operations (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income from discontinued operations, net of tax	$ 1,789	$ 489	$ 452
Income from discontinued operations attributable to noncontrolling interest, net of tax	219	191	165
Income from discontinued operations	1,570	298	287
Discontinued Operations, Disposed of by Sale | Residential and Light Commercial HVAC Business
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net sales	3,790	4,466	4,462
Cost of goods sold	2,881	3,300	3,295
Gross profit	909	1,166	1,167
Disposal Group, Including Discontinued Operation, General And Administrative Expense, Including Adjustments	(2,008)
Selling, general and administrative expenses		761	794
Restructuring and impairment costs	30	34	15
Net financing charges	5	17	23
Equity income	240	276	262
Income from discontinued operations before income taxes	3,122	630	597
Provision for income taxes on discontinued operations	1,333	141	145
Income from discontinued operations, net of tax	1,789	489	452
Income from discontinued operations attributable to noncontrolling interest, net of tax	219	191	165
Income from discontinued operations	$ 1,570	$ 298	$ 287