Debt (Narrative) (Details) - USD ($)	1 Months Ended	12 Months Ended
	Mar. 31, 2024	Sep. 30, 2024	Mar. 28, 2024	Feb. 06, 2024	Sep. 30, 2023
Debt Instrument [Line Items]
Total debt		$ 14,227,900,000			$ 10,305,800,000
Current portion of long-term debt		611,400,000			615,000,000.0
Deferred financing charges and discounts		304,500,000			165,700,000
Long-term debt, principal amount		14,485,500,000			10,292,500,000
Senior Notes | Green Bonds
Debt Instrument [Line Items]
Aggregate principal amount				$ 2,500,000,000
Deferred financing charges and discounts				$ 20,000,000
Long-term debt, principal amount		2,500,000,000
Bonds | Saudi Riyal Loan Facility variable-rate 7.35% due 2027
Debt Instrument [Line Items]
Long-term debt, principal amount		451,100,000			451,100,000
Revolving credit agreement | 364-Day Credit Agreement | Line of Credit
Debt Instrument [Line Items]
Term of credit facility (in years)	364 days
Maximum borrowing capacity		500,000,000.0
Credit facility, amount borrowed and outstanding		0
Revolving credit agreement | Line of Credit | 2024 Credit Agreement
Debt Instrument [Line Items]
Term of credit facility (in years)	5 years
Maximum borrowing capacity		3,000,000,000
Credit facility, amount borrowed and outstanding		0
Revolving credit agreement | Line of Credit | 2021 Credit Agreement
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 2,750,000,000
Credit facility, amount borrowed and outstanding			$ 0
CreditFacilityEarlyTerminationFee		0
Foreign credit facilities | Credit Facilities, Foreign Subsidiaries
Debt Instrument [Line Items]
Maximum borrowing capacity		1,223,900,000
Credit facility, amount borrowed and outstanding		1,129,000,000			1,041,400,000
Related Party
Debt Instrument [Line Items]
Total debt		304,400,000			328,300,000
Current portion of long-term debt		$ 200,000,000.0			$ 177,600,000