Debt (Committed Credit Facilities) (Details) - USD ($)	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024
Debt Instrument [Line Items]
Long-term debt, principal amount	$ 17,996,000,000	$ 14,485,500,000
Saudi Riyal Loan Facility 2.00% due 2026 to 2034 | Bonds
Debt Instrument [Line Items]
Interest rate		2.00%
Long-term debt, principal amount	0	$ 222,200,000
Saudi Riyal Loan Facility 2.00% due 2026 to 2034 | Bonds | Blue Hydrogen Industrial Gases Company
Debt Instrument [Line Items]
Interest rate		2.00%
Long-term debt, principal amount		$ 222,200,000
Saudi Riyal Loan Facility variable-rate 7.35% due 2027 | Bonds
Debt Instrument [Line Items]
Interest rate, variable percentage		7.35%
Long-term debt, principal amount	$ 0	$ 451,100,000
Saudi Riyal Loan Facility variable-rate 7.35% due 2027 | Bonds | Blue Hydrogen Industrial Gases Company
Debt Instrument [Line Items]
Interest rate, variable percentage		7.35%
Long-term debt, principal amount		$ 451,100,000
Revolving credit agreement | 364-Day Credit Agreement | Line of Credit
Debt Instrument [Line Items]
Term of credit facility (in days or years)	364 days
Credit facility, maximum borrowing capacity	$ 500,000,000
Credit facility, amount borrowed and outstanding	$ 0	0
Revolving credit agreement | Five Year Credit Agreement | Line of Credit
Debt Instrument [Line Items]
Term of credit facility (in days or years)	5 years
Credit facility, maximum borrowing capacity	$ 3,000,000,000
Credit facility, amount borrowed and outstanding	0	0
Foreign credit facilities | Credit Facilities, Foreign Subsidiaries
Debt Instrument [Line Items]
Credit facility, maximum borrowing capacity	394,000,000.0	1,200,000,000
Credit facility, amount borrowed and outstanding	$ 394,000,000.0	$ 1,100,000,000