Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Gross Deferred Tax Assets
Tax loss carryforwards	$ 0.5	$ 13.2
Tax credit carryforwards	0.9	64.2
Retirement benefits and compensation accruals	10.9	7.6
Reserves and accruals	1.6	8.4
Other	1.5	3.3
Valuation allowance	(0.9)	(55.6)
Deferred Tax Assets	14.5	41.1
Gross Deferred Tax Liabilities
Intangible assets	9.1	41.0
Plant and equipment	22.9	22.2
Unremitted earnings of foreign entities	0.7	2.3
Partnership investments	0.8	1.3
Other	0.2	6.3
Deferred Tax Liabilities	33.7	73.1
Net Deferred Income Tax Liability	$ 19.2	$ 32.0