Variable Interest Entities- Project Financing (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Variable Interest Entity [Line Items]
Long-term debt, principal amount	$ 14,485.5	$ 10,292.5
Deferred financing charges and discounts	304.5	165.7
Short-term borrowings	83.5	259.5
Variable Interest Entity, Primary Beneficiary | NEOM Green Hydrogen Company
Variable Interest Entity [Line Items]
Project financing fees	4.6	58.8
Short-term borrowings	51.6	0.0
Variable Interest Entity, Primary Beneficiary | Nonrecourse | NEOM Green Hydrogen Company
Variable Interest Entity [Line Items]
Long-term debt, principal amount	3,271.8	1,364.8
Deferred financing charges and discounts	218.5	90.4
Long-term debt	3,053.3	1,274.4
Variable Interest Entity, Primary Beneficiary | Nonrecourse | NEOM Green Hydrogen Company | Payable in U.S. Dollars
Variable Interest Entity [Line Items]
Long-term debt, principal amount	$ 2,536.6	$ 1,233.4
Variable Interest Entity, Primary Beneficiary | U.S. Dollar Variable Rate Facility, 6.17% due 2027-2053 | Nonrecourse | NEOM Green Hydrogen Company
Variable Interest Entity [Line Items]
Interest rate, variable percentage	6.17%
Variable Interest Entity, Primary Beneficiary | U.S. Dollar Variable Rate Facility, 6.17% due 2027-2053 | Nonrecourse | NEOM Green Hydrogen Company | Secured Overnight Financing Rate (SOFR)
Variable Interest Entity [Line Items]
Annual margin	1.31%	0.96%
Variable Interest Entity, Primary Beneficiary | U.S. Dollar Variable Rate Facility, 6.17% due 2027-2053 | Nonrecourse | NEOM Green Hydrogen Company | Payable in U.S. Dollars
Variable Interest Entity [Line Items]
Long-term debt, principal amount	$ 1,945.2	$ 1,094.9
Variable Interest Entity, Primary Beneficiary | U.S. Dollar Variable Rate Facility, 5.82% Due 2027-2041 | Nonrecourse | NEOM Green Hydrogen Company
Variable Interest Entity [Line Items]
Interest rate, variable percentage	5.82%
Variable Interest Entity, Primary Beneficiary | U.S. Dollar Variable Rate Facility, 5.82% Due 2027-2041 | Nonrecourse | NEOM Green Hydrogen Company | Payable in U.S. Dollars
Variable Interest Entity [Line Items]
Long-term debt, principal amount	$ 345.5	0.0
Variable Interest Entity, Primary Beneficiary | U.S. Dollar Loan Facility 5.00% due 2027-2053 | Nonrecourse | NEOM Green Hydrogen Company
Variable Interest Entity [Line Items]
Interest rate, stated percentage	5.00%
Variable Interest Entity, Primary Beneficiary | U.S. Dollar Loan Facility 5.00% due 2027-2053 | Nonrecourse | NEOM Green Hydrogen Company | Payable in U.S. Dollars
Variable Interest Entity [Line Items]
Long-term debt, principal amount	$ 245.9	138.5
Variable Interest Entity, Primary Beneficiary | Saudi Riyal Loan Facility 6.62% due 2025-2027 | Nonrecourse | NEOM Green Hydrogen Company | Saudi Arabian Interbank Offered Rate (SAIBOR)
Variable Interest Entity [Line Items]
Annual margin	0.80%
Variable Interest Entity, Primary Beneficiary | Saudi Riyal Loan Facility 6.62% due 2025-2027 | Nonrecourse | NEOM Green Hydrogen Company | Other Currency
Variable Interest Entity [Line Items]
Interest rate, variable percentage	6.69%
Long-term debt, principal amount	$ 0.0	131.4
Variable Interest Entity, Primary Beneficiary | Saudi Riyal Loan Facility variable-rate 2.00% due 2028 to 2041 | Nonrecourse | NEOM Green Hydrogen Company | Other Currency
Variable Interest Entity [Line Items]
Interest rate, variable percentage	2.00%
Long-term debt, principal amount	$ 735.2	$ 0.0
Variable Interest Entity, Primary Beneficiary | Saudi Riyal Loan Facility Variable-Rate 6.21% | NEOM Green Hydrogen Company
Variable Interest Entity [Line Items]
Interest rate, variable percentage	6.21%
Short-term borrowings	$ 51.6