Variable Interest Entities - JIGPC Joint Venture (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2021	Jun. 30, 2025	Sep. 30, 2024
Schedule of Equity Method Investments [Line Items]
Investment in net assets of and advances to equity affiliates		$ 5,227.8	$ 4,792.5
Jazan Integrated Gasification and Power Company ("JIGPC")
Schedule of Equity Method Investments [Line Items]
Ownership interest percentage		55.00%
Ownership percentage attributable to noncontrolling partner (in percent)		4.00%
Investment balance		$ 3,000.0	$ 2,900.0
Investment in net assets of and advances to equity affiliates		$ 115.0
Jazan Integrated Gasification and Power Company ("JIGPC") | Aramco
Schedule of Equity Method Investments [Line Items]
Term of project agreement (in years)	25 years