Accumulated Other Comprehensive Loss - Changes in Accumulated Other Comprehensive Loss by Component (Details) - USD ($) shares in Thousands, $ in Millions	3 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ 3,675.0	$ 3,743.0
Other comprehensive (loss) income before reclassifications	(105.0)	66.0
Amounts reclassified from accumulated other comprehensive loss	5.0	(6.0)
Other comprehensive (loss) income	(100.0)	60.0
Balance at end of period	$ 3,556.0	3,787.0
Share retirement	40,000
AOCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ (772.0)	(790.0)
Other comprehensive (loss) income	(100.0)	60.0
Balance at end of period	(872.0)	(730.0)
Pension and other postretirement benefit plan adjustments, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(431.0)	(407.0)
Other comprehensive (loss) income before reclassifications	0.0	0.0
Amounts reclassified from accumulated other comprehensive loss	5.0	0.0
Other comprehensive (loss) income	5.0	0.0
Balance at end of period	(426.0)	(407.0)
Accumulated currency translation adjustments, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(296.0)	(365.0)
Other comprehensive (loss) income before reclassifications	(130.0)	84.0
Amounts reclassified from accumulated other comprehensive loss	0.0	0.0
Other comprehensive (loss) income	(130.0)	84.0
Balance at end of period	(426.0)	(281.0)
Net unrealized losses (gains) on cash flow hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(45.0)	(18.0)
Other comprehensive (loss) income before reclassifications	25.0	(18.0)
Amounts reclassified from accumulated other comprehensive loss	0.0	(6.0)
Other comprehensive (loss) income	25.0	(24.0)
Balance at end of period	$ (20.0)	$ (42.0)