Discontinued Operations (Schedule of Operating Results) (Details) - USD ($) $ in Millions		3 Months Ended									12 Months Ended
		Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (loss) from Discontinued Operations, net of tax		$ 0.0	$ 0.0	$ 0.0	$ 0.0	$ 0.0	$ 43.2	$ 0.0	$ (1.0)		$ 0.0	$ 42.2	$ 1,866.0
Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sales													254.8
Cost of sales													196.1
Selling and administrative													23.2
Research and development													5.1
Other income (expense), net													(1.7)
Operating Income (Loss)													28.7
Equity affiliates' income													0.3
Income (Loss) Before Taxes													29.0
Income tax benefit	[1]												(56.5)
Income (Loss) From Operations of Discontinued Operations, net of tax													85.5
Gain (Loss) on disposal of business, net of tax	[2]												1,780.5
Income (loss) from Discontinued Operations, net of tax												42.2	1,866.0
Performance Materials Division (PMD) | Discontinued Operations, Held-for-sale or Disposed of by Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sales													254.8
Cost of sales													182.3
Selling and administrative													22.5
Research and development													5.1
Other income (expense), net													0.3
Operating Income (Loss)													45.2
Equity affiliates' income													0.3
Income (Loss) Before Taxes													45.5
Income tax benefit	[1]												(50.8)
Income (Loss) From Operations of Discontinued Operations, net of tax													96.3
Gain (Loss) on disposal of business, net of tax	[2]												1,827.6
Income (loss) from Discontinued Operations, net of tax													1,923.9
Valuation allowance adjustment effect on income tax provision										$ 69.0
Gross expense for income tax reserves included in provision for gain on disposal													28.0
Net expense for income tax reserves included in provision for gain on disposal													21.0
Energy-from-Waste (EfW) | Discontinued Operations, Held-for-sale or Disposed of by Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sales	[3]												0.0
Cost of sales	[3]												13.8
Selling and administrative	[3]												0.7
Research and development	[3]												0.0
Other income (expense), net	[3]												(2.0)
Operating Income (Loss)	[3]												(16.5)
Equity affiliates' income	[3]												0.0
Income (Loss) Before Taxes	[3]												(16.5)
Income tax benefit	[1],[3]												(5.7)
Income (Loss) From Operations of Discontinued Operations, net of tax	[3]												(10.8)
Gain (Loss) on disposal of business, net of tax	[2],[3]												(47.1)
Income (loss) from Discontinued Operations, net of tax												$ (1.0)	$ (57.9)	[3]

[1] As a result of the expected gain on the sale of PMD, we released valuation allowances related to capital loss and net operating loss carryforwards primarily during the first quarter of 2017 that favorably impacted our income tax provision within discontinued operations by approximately $69.

[2] After-tax gain on sale of $1,827.6 included expense for income tax reserves for uncertain tax positions of $28.0 gross ($21.0 net) in various jurisdictions.

[3] The loss from operations of discontinued operations for EfW primarily related to costs incurred for ongoing project exit activities, administrative costs, and land lease obligations.