Discontinued Operations (Narrative) (Details)			3 Months Ended			6 Months Ended	12 Months Ended
	Jan. 03, 2017 USD ($)	Oct. 01, 2016	Mar. 31, 2017 USD ($) $ / shares	Dec. 31, 2016 USD ($)	Mar. 31, 2016 USD ($)	Mar. 31, 2017 USD ($)	Sep. 30, 2016 USD ($)
Electronic Materials Division [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Distribution ratio of common stock in spin-off		0.5
Electronic Materials Division [Member] | Minimum [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Transition services agreement months from divestiture not to exceed		12 months
Electronic Materials Division [Member] | Maximum [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Transition services agreement months from divestiture not to exceed		24 months
Performance Materials Division [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale	$ 3,800,000,000
Gain on sale, before-tax			$ 2,870,000,000
Gain on sale, after-tax			$ 1,833,000,000
Gain on sale, after-tax, per share | $ / shares			$ 8.34
Performance Materials Division [Member] | Maximum [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Transition services agreement months from divestiture not to exceed	12 months
Energy-from-Waste [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss on disposal, before-tax				$ 59,300,000	$ 945,700,000	$ 59,300,000	$ 945,700,000
Loss on disposal, net of tax				47,100,000	$ 846,600,000
Accrual for actions to dispose of business			$ 64,900,000			64,900,000	12,200,000
Change to estimates of loss on disposal			0
Energy-from-Waste [Member] | Continuing Operations [Member] | Other Noncurrent Liabilities [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Accrual for actions to dispose of business			60,000,000			60,000,000
Energy-from-Waste [Member] | Discontinued Operations [Member] | Current Liabilities [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Accrual for actions to dispose of business			5,000,000			5,000,000
Energy-from-Waste [Member] | Asset Actions [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss on disposal, before-tax				6,300,000		6,300,000	913,500,000
Accrual for actions to dispose of business			0			0	0
Energy-from-Waste [Member] | Contract Actions/other [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss on disposal, before-tax				$ 53,000,000		53,000,000	32,200,000
Accrual for actions to dispose of business			$ 64,900,000			$ 64,900,000	$ 12,200,000