Accumulated Other Comprehensive Loss - Changes in Accumulated Other Comprehensive Loss by Component (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ 3,711	$ 3,675
Other comprehensive (loss) income before reclassifications	30	(105)
Amounts reclassified from accumulated other comprehensive loss	3	5
Other comprehensive income (loss)	33	(100)
Balance at end of period	3,800	3,556
AOCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(657)	(772)
Other comprehensive income (loss)	33	(100)
Balance at end of period	(624)	(872)
Pension and other postretirement benefit plan adjustments, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(335)	(431)
Other comprehensive (loss) income before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive loss	3	5
Other comprehensive income (loss)	3	5
Balance at end of period	(332)	(426)
Accumulated currency translation adjustments, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(281)	(297)
Other comprehensive (loss) income before reclassifications	27	(129)
Amounts reclassified from accumulated other comprehensive loss	0	0
Other comprehensive income (loss)	27	(129)
Balance at end of period	(254)	(426)
Net unrealized losses (gains) on cash flow hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(41)	(44)
Other comprehensive (loss) income before reclassifications	3	24
Amounts reclassified from accumulated other comprehensive loss	0	0
Other comprehensive income (loss)	3	24
Balance at end of period	$ (38)	$ (20)