Discontinued Operations (Schedule of Assets and Liabilities) (Details) - USD ($) $ in Millions	Mar. 31, 2017		Sep. 30, 2016	Mar. 31, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash and cash items	$ 0.0			$ 26.4
Total Current Assets	9.8		$ 926.2
Total Noncurrent Assets	0.0		1,042.3
Total Assets	9.8		1,968.5
Total Current Liabilities	24.1		211.8
Total Noncurrent Liabilities	0.0		1,095.5
Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash and cash items			208.1
Trade receivables, net			293.7
Inventories			364.9
Plant and equipment, net	9.6		18.2
Other receivables and current assets	0.2		41.3
Total Current Assets	9.8		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	9.8		1,968.5
Payables and accrued liabilities	24.1	[1]	177.3
Accrued income taxes			28.7
Current portion of long-term debt			5.8
Total Current Liabilities	24.1		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	24.1		1,307.3
Discontinued Operations [Member] | Electronic Materials Division [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
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
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
Discontinued Operations [Member] | Performance Materials Division [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
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	0.0		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
Payables and accrued liabilities	17.4	[1]	72.5
Accrued income taxes			6.0
Current portion of long-term debt			0.0
Total Current Liabilities	17.4		78.5
Long-term debt			0.0
Deferred income taxes			6.4
Other noncurrent liabilities			9.6
Total Noncurrent Liabilities			16.0
Total Liabilities	17.4		94.5
Discontinued Operations [Member] | Energy-from-Waste [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash and cash items			0.0
Trade receivables, net			0.0
Inventories			0.0
Plant and equipment, net	9.6		18.2
Other receivables and current assets	0.2		1.2
Total Current Assets	9.8		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	9.8		19.4
Payables and accrued liabilities	6.7	[1]	19.0
Accrued income taxes			0.0
Current portion of long-term debt			0.0
Total Current Liabilities	6.7		19.0
Long-term debt			0.0
Deferred income taxes			0.0
Other noncurrent liabilities			0.0
Total Noncurrent Liabilities			0.0
Total Liabilities	$ 6.7		$ 19.0

[1] Includes reserves associated with disposition of businesses.