Business and Asset Actions - Project Exit Costs (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2025	Mar. 31, 2025	Jun. 30, 2025	Sep. 30, 2024
Restructuring Cost and Reserve [Line Items]
Plant and equipment, net	$ 25,640.0		$ 25,640.0	$ 23,370.9
Project Exit Costs
Restructuring Cost and Reserve [Line Items]
Project exit costs			2,885.9
Noncash expenses			(2,468.2)
Cash payments			(100.4)
Currency translation adjustment			8.5
Accrual for unpaid benefits reflected in "Payables and Accrued Liabilities"	325.8		325.8
Estimated effect on cash flows, total	425.0
Project Exit Costs | Fair Value, Nonrecurring
Restructuring Cost and Reserve [Line Items]
Plant and equipment, net	22.5	$ 22.5	22.5
Operating Income (Loss) | Project Exit Costs
Restructuring Cost and Reserve [Line Items]
Project exit costs	$ 24.1	$ 2,861.8	2,885.9
Income (Loss) from Equity Method Investments | Project Exit Costs
Restructuring Cost and Reserve [Line Items]
Project exit costs			$ 6.8