Accumulated Other Comprehensive Loss (Income) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Dec. 31, 2018	Dec. 31, 2019	Sep. 30, 2018
Foreign Currency Translation Adjustments
Beginning balance	$ (78.9)	$ (78.9)	$ (78.6)
Change during the period		2.4	(0.3)
Ending balance	(78.9)	(76.5)	(78.9)
Change in Fair Value of Hedging Instrument
Beginning balance	0.1	(0.1)
Change during the period	(0.2)	1.5	0.1
Ending balance	(0.1)	1.4	0.1
Unrecognized Pension Benefit Costs
Beginning balance	20.3	23.1	25.5
Change during the period	2.8	6.9	(5.2)
Ending balance	23.1	30.0	20.3
Accumulated Other Comprehensive (Income)
Beginning balance	58.5	(55.9)	(53.1)
Change during the period	2.6	10.8	(5.4)
Ending balance	$ (55.9)	$ 45.1	$ 58.5

Amount, after tax, of accumulated other comprehensive (income) loss for defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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Accumulated adjustment, net of tax, that results from the process of translating subsidiary financial statements and foreign equity investments into the reporting currency from the functional currency of the reporting entity, net of reclassification of realized foreign currency translation gains or losses.

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Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

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Amount, after tax, of accumulated gain (loss) on derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

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Amount of tax expense (benefit), after reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature, attributable to parent entity.

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Amount of tax expense (benefit) for reclassification of gain (loss) from accumulated other comprehensive income (AOCI) for derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

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