Major Accounting Policies (Narrative) (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Accounting Policies [Abstract]
Assets of discontinued operations		$ 0	$ 0
Liabilities of discontinued operations		0	0
Environmental expenditures		18,600,000	18,300,000	$ 14,200,000
Pre-tax loss from discontinued operations	$ 19,000,000.0		19,000,000.0
Capitalized interest		28,300,000	15,900,000	13,500,000
Asset retirement obligations		269,600,000	241,400,000	208,200,000
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, residual value		0
Other Non-Operating Income (Expense), Net
Finite-Lived Intangible Assets [Line Items]
Excluded components recognized within earnings		31,000,000.0	33,500,000
Excluded components recognized within earnings		$ 31,000,000.0	$ 33,500,000
Interest Expense
Finite-Lived Intangible Assets [Line Items]
Excluded components recognized within earnings				33,300,000
Excluded components recognized within earnings				$ 33,300,000
Computer software costs | Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life		3 years
Computer software costs | Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life		5 years
Customer relationships | Minimum
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, useful life		5 years
Customer relationships | Maximum
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, useful life		25 years
Patents and technology | Minimum
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, useful life		5 years
Patents and technology | Maximum
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, useful life		15 years
Land Use Rights
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, useful life		50 years