Major Accounting Policies (Narrative) (Details) - USD ($)	3 Months Ended																12 Months Ended
	Sep. 30, 2017		Jun. 30, 2017	[1]	Mar. 31, 2017	[1]	Dec. 31, 2016	[1]	Sep. 30, 2016		Jun. 30, 2016	[1]	Mar. 31, 2016	[1]	Dec. 31, 2015	[1]	Sep. 30, 2017		Sep. 30, 2016		Sep. 30, 2015
Accounting Policies [Abstract]
Environmental expenditures																	$ 11,400,000		$ 12,200,000		$ 11,800,000
Allowance for doubtful accounts	$ 93,500,000								$ 55,300,000								93,500,000		55,300,000
Provision for doubtful accounts																	45,800,000		21,800,000		25,900,000
Capitalized interest	19,000,000								32,700,000								19,000,000		32,700,000		49,100,000
Asset retirement obligations	144,700,000								119,900,000								$ 144,700,000		119,900,000		109,400,000
Period for reallocation of purchase price																	1 year
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, residual value	0																$ 0
Change in Accounting Estimate [Line Items]
Operating income	$ 455,700,000	[1]	$ 252,600,000		$ 391,200,000		$ 328,100,000		$ 391,000,000	[1]	$ 394,600,000		$ 371,600,000		$ 372,500,000		$ 1,427,600,000	[1]	1,529,700,000	[1]	$ 1,233,200,000
Software and Software Development Costs | Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life																	3 years
Software and Software Development Costs | Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life																	10 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
Contracts accounted for under percentage of completion
Change in Accounting Estimate [Line Items]
Operating income																	$ 27,000,000		$ 20,000,000

[1] Changes in estimates on projects accounted for under the percentage of completion method favorably impacted income by approximately $27 in fiscal year 2017 and $20 in fiscal year 2016, primarily during the fourth quarter. For additional information, see Note 1, Major Accounting Policies (Revenue Recognition).