Debt (Narrative) (Details) € in Millions		1 Months Ended	12 Months Ended
	Mar. 31, 2021	May 31, 2023 USD ($)	Sep. 30, 2023 USD ($)	Mar. 03, 2023 USD ($)	Mar. 03, 2023 EUR (€)	Sep. 30, 2022 USD ($)
Debt Instrument [Line Items]
Total debt			$ 10,305,800,000			$ 7,644,800,000
Current portion of long-term debt			615,000,000.0			548,300,000
Deferred financing charges and discounts			165,700,000			45,400,000
Long-term debt, principal amount			$ 10,292,500,000			7,309,300,000
NEOM Green Hydrogen Project Financing, Primary | Nonrecourse | NEOM Green Hydrogen Company
Debt Instrument [Line Items]
Project financing, maximum borrowing capacity		$ 6,100,000,000
Amount of debt funding, percent			73.00%
NEOM Green Hydrogen Project Financing, Working Capital | Nonrecourse | NEOM Green Hydrogen Company
Debt Instrument [Line Items]
Project financing, maximum borrowing capacity		$ 500,000,000
NEOM Green Hydrogen Project Financing | Nonrecourse | NEOM Green Hydrogen Company
Debt Instrument [Line Items]
Long-term debt, principal amount			$ 1,400,000,000
Senior Notes | Green Bonds
Debt Instrument [Line Items]
Aggregate principal amount				$ 600,000,000	€ 700
Deferred financing charges and discounts				$ 15,000,000
Bonds | Saudi Riyal Loan Facility variable-rate 7.00% due 2027
Debt Instrument [Line Items]
Long-term debt, principal amount			$ 451,100,000			0
Annual margin			1.35%
Bonds | Saudi Riyal Loan Facility variable-rate 4.10% due 2023
Debt Instrument [Line Items]
Long-term debt, principal amount			$ 0			195,600,000
Revolving credit agreement | 2021 Credit Agreement
Debt Instrument [Line Items]
Term of credit facility (in years)	5 years
Maximum borrowing capacity			2,750,000,000
Credit facility, amount borrowed and outstanding			$ 0
Revolving credit agreement | Maximum | 2021 Credit Agreement
Debt Instrument [Line Items]
Debt covenant, maximum ratio of total debt to capitalization			70.00%
Foreign credit facilities | Credit Facilities, Foreign Subsidiaries
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 1,596,800,000
Credit facility, amount borrowed and outstanding			1,041,400,000			457,500,000
Related Party
Debt Instrument [Line Items]
Total debt			328,300,000			781,000,000.0
Current portion of long-term debt			$ 177,600,000			$ 129,000,000.0