Discontinued Operations (Narrative) (Details) - USD ($) $ / shares in Units, $ 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
Liabilities associated with EfW		57.8				63.3					57.8	63.3
Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (loss) from discontinued operations, net of tax												42.2	1,866.0
Assets of discontinued operations		0.0				0.0					0.0	0.0
Liabilities of discontinued operations		$ 0.0				$ 0.0					$ 0.0	0.0
Gain on sale, after tax	[1]												1,780.5
European Homecare business | Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Tax benefit related to settlement and release of reserves												25.6
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]
Income (loss) from discontinued operations, net of tax													1,923.9
Adjustment to prior gain (loss) on disposal, net of tax												17.6
Gain on sale, before tax													2,870.0
Gain on sale, after tax	[1]												$ 1,827.6
Gain on sale, after tax, per share													$ 8.32
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]
Income (loss) from discontinued operations, net of tax												$ (1.0)	$ (57.9)	[2]
Gain on sale, after tax	[1],[2]												$ (47.1)
Loss on disposal, before tax										$ 59.3
Loss on disposal, after tax										$ 47.1

[1] 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.

[2] 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.