Discontinued Operations (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions			3 Months Ended
		Jan. 03, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2017	Sep. 30, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Current assets of discontinued operations					$ 10.2	$ 10.2
Current liabilities of discontinued operations					13.6	15.7
Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale, after-tax			$ (47.1)
Current liabilities of discontinued operations					13.6	15.7
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]
Proceeds from sale		$ 3,800.0
Gain on sale, before-tax		2,870.0
Gain on sale, after-tax		$ 1,828.0	0.0
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]
Gain on sale, after-tax	[1]		(47.1)
Loss on disposal, before-tax			59.3	$ 945.7
Loss on disposal, after tax			$ 47.1	$ 846.6
Current assets of discontinued operations					$ 10.2	$ 10.2

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