Discontinued Operations (Schedule of Assets and Liabilities) (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Current Assets
Cash and cash items	$ 0.0	$ 208.1	$ 23.3
Total Current Assets	10.2	926.2
Total Noncurrent Assets	0.0	1,042.3
Current Liabilities
Total Current Liabilities	15.7	211.8
Total Noncurrent Liabilities	0.0	1,095.5
Discontinued Operations
Current Assets
Cash and cash items		208.1
Trade receivables, net		293.7
Inventories		364.9
Plant and equipment, net	10.2	18.2
Other receivables and current assets		41.3
Total Current Assets	10.2	926.2
Plant and equipment, net		593.0
Goodwill, net		305.0
Intangible assets, net		100.1
Other noncurrent assets		44.2
Total Noncurrent Assets		1,042.3
Total Assets	10.2	1,968.5
Current Liabilities
Payables and accrued liabilities	15.7	177.3
Accrued income taxes		28.7
Current portion of long-term debt		5.8
Total Current Liabilities	15.7	211.8
Long-term debt		981.8
Deferred income taxes		56.7
Other noncurrent liabilities		57.0
Total Noncurrent Liabilities		1,095.5
Total Liabilities	15.7	1,307.3
Electronic Materials Division (EMD) | Discontinued Operations, Spinoff
Current Assets
Cash and cash items		170.6
Trade receivables, net		134.7
Inventories		138.1
Plant and equipment, net		0.0
Other receivables and current assets		34.5
Total Current Assets		477.9
Plant and equipment, net		296.5
Goodwill, net		180.0
Intangible assets, net		75.1
Other noncurrent assets		37.5
Total Noncurrent Assets		589.1
Total Assets		1,067.0
Current Liabilities
Payables and accrued liabilities		85.8
Accrued income taxes		22.7
Current portion of long-term debt		5.8
Total Current Liabilities		114.3
Long-term debt		981.8
Deferred income taxes		50.3
Other noncurrent liabilities		47.4
Total Noncurrent Liabilities		1,079.5
Total Liabilities		1,193.8
Performance Materials Division (PMD) | Discontinued Operations, Held-for-sale or Disposed of by Sale
Current Assets
Cash and cash items		37.5
Trade receivables, net		159.0
Inventories		226.8
Plant and equipment, net	0.0	0.0
Other receivables and current assets		5.6
Total Current Assets	0.0	428.9
Plant and equipment, net		296.5
Goodwill, net		125.0
Intangible assets, net		25.0
Other noncurrent assets		6.7
Total Noncurrent Assets		453.2
Total Assets	0.0	882.1
Current Liabilities
Payables and accrued liabilities	9.2	72.5
Accrued income taxes		6.0
Current portion of long-term debt		0.0
Total Current Liabilities	9.2	78.5
Long-term debt		0.0
Deferred income taxes		6.4
Other noncurrent liabilities		9.6
Total Noncurrent Liabilities		16.0
Total Liabilities	9.2	94.5
Energy-from-Waste (EfW) | Discontinued Operations, Held-for-sale or Disposed of by Sale
Current Assets
Cash and cash items		0.0
Trade receivables, net		0.0
Inventories		0.0
Plant and equipment, net	10.2	18.2
Other receivables and current assets		1.2
Total Current Assets	10.2	19.4
Plant and equipment, net		0.0
Goodwill, net		0.0
Intangible assets, net		0.0
Other noncurrent assets		0.0
Total Noncurrent Assets		0.0
Total Assets	10.2	19.4
Current Liabilities
Payables and accrued liabilities	6.5	19.0
Accrued income taxes		0.0
Current portion of long-term debt		0.0
Total Current Liabilities	6.5	19.0
Long-term debt		0.0
Deferred income taxes		0.0
Other noncurrent liabilities		0.0
Total Noncurrent Liabilities		0.0
Total Liabilities	$ 6.5	$ 19.0