(Litigation) (Narrative) (Details) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2017 USD ($)	Dec. 31, 2004 USD ($) resident	Sep. 30, 2017 USD ($)	Jan. 01, 2012 USD ($) water_district
PFOA Matters [Member]
Loss Contingencies [Line Items]
Accrual balance			$ 15.0
Indemnification assets			15.0
Period for sharing for PFOA Liabilities	5 years
Limited Sharing Of Potential Future Liabilities, Maximum Annual Liability Threshold, paid by DuPont	$ 25.0
PFOA Matters [Member] | Chemours [Member]
Loss Contingencies [Line Items]
Additional annual PFOA liabilities for the next five years paid by Chemours	25.0
PFOA Matters: Drinking Water Actions [Member]
Loss Contingencies [Line Items]
Binding settlement agreement, class size | resident		80,000
Liability For Medical Monitoring Program, Threshold		$ 235.0
Escrow deposit				$ 1.0
Escrow amount disbursed (less than)			$ 1.0
Number Of Water Districts Receiving Water Treatment | water_district				6
PFOA Matters: Drinking Water Actions [Member] | Payment for Plaintiffs Attorney Fees [Member]
Loss Contingencies [Line Items]
Litigation Settlement, Expense		23.0
PFOA Matters: Drinking Water Actions [Member] | Payment to fund community health project [Member]
Loss Contingencies [Line Items]
Settlement payments		$ 70.0
PFOA Matters: Multi-District Litigation [Member]
Loss Contingencies [Line Items]
Lawsuits alleging personal injury			3,550
MDL Settlement Amount	$ 670.7
PFOA Matters [Member]
Loss Contingencies [Line Items]
Accrual balance			$ 15.0