Debt (Tax-Exempt Financings) (Details) - USD ($)	3 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Long-term debt	$ 9,678,300,000
Restricted cash and marketable securities	139,000,000
Tax-exempt: 2023 - 2051
Debt Instrument [Line Items]
Long-term debt	1,181,500,000	$ 1,104,700,000
Principal amount	205,000,000	60,000,000
Restricted cash and marketable securities	12,400,000
Line Of Credit Due August 2026
Debt Instrument [Line Items]
Long-term debt	24,300,000	$ 0
Solid Waste Disposal Revenue Bonds
Debt Instrument [Line Items]
Principal amount	30,000,000
Costs incurred and reimbursed	17,200,000
Line of Credit | Line Of Credit Due August 2026
Debt Instrument [Line Items]
Credit facility maximum borrowing capacity	$ 3,000,000,000