Major Accounting Policies (Narrative) (Details) - USD ($)	3 Months Ended	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Accounting Policies [Abstract]
Environmental expenditures		$ 14,200,000	$ 12,800,000	$ 11,400,000
Allowance for doubtful accounts	$ 91,300,000	88,200,000	91,300,000
Provision for doubtful accounts		48,800,000	24,000,000.0	45,800,000
Capitalized interest	19,500,000	13,500,000	19,500,000	19,000,000.0
Asset retirement obligations	190,400,000	208,200,000	190,400,000	144,700,000
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in cost of sales		(5,975,500,000)	(6,189,500,000)	$ (5,751,500,000)
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, residual value		$ 0
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
Change in Inventory Valuation Method
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in cost of sales	$ 24,100,000		$ 24,100,000