Income Taxes (Components of the Income Taxes Provision) (Details) - USD ($) $ in Millions	3 Months Ended												12 Months Ended
	Sep. 30, 2017	[1]	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	[2]	Jun. 30, 2016	[2]	Mar. 31, 2016	[2]	Dec. 31, 2015	Sep. 30, 2017		Sep. 30, 2016		Sep. 30, 2015
Current Tax Provision
Federal													$ 62.8		$ 171.0		$ 117.0
State													7.0		21.2		8.1
Foreign													229.1		178.6		165.7
Current Tax Provision													298.9		370.8		290.8
Deferred Tax Provision
Federal													1.4		45.0		1.5
State													6.0		2.8		17.8
Foreign													(45.4)		14.0		(9.9)
Deferred Tax Provision													(38.0)		61.8		9.4
Income tax provision	$ (1.3)		$ 89.3	$ 94.5	$ 78.4	$ 96.8		$ 145.9		$ 93.5		$ 96.4	$ 260.9	[1]	$ 432.6	[2]	$ 300.2

[1] Includes the impact of a tax election benefit related to a non-U.S. subsidiary. For additional information, see Note 22, Income Taxes.

[2] Includes income tax expense for tax costs associated with business separation. For additional information, see Note 4, Materials Technologies Separation.