Equity Affiliates (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2025	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Schedule of Equity Method Investments [Line Items]
Investment in net assets of and advances to equity affiliates		$ 5,366.1	$ 4,792.5
Dividends and other distributions received from equity affiliates		385.5	441.7	$ 344.3
Goodwill associated with affiliate companies accounted for by equity method		34.5	38.7
Project exit-related impairment of equity method investment		6.8	0.0	0.0
Jazan Integrated Gasification and Power Company ("JIGPC")
Schedule of Equity Method Investments [Line Items]
Investment in net assets of and advances to equity affiliates		$ 115.0
Payments for equity investment	$ 115.0			908.0	$ 1,600.0
Ownership interest percentage		55.00%
Investment balance		$ 3,100.0	$ 2,900.0
Ownership percentage attributable to noncontrolling partner		4.00%
Jazan Integrated Gasification and Power Company ("JIGPC") | Non-controlling Interests
Schedule of Equity Method Investments [Line Items]
Payments for equity investment				$ 73.0	$ 130.0
Bangkok Industrial Gases Co., Ltd.
Schedule of Equity Method Investments [Line Items]
Ownership interest percentage		49.00%