Related Party Transactions Dow Intercompany Transactions (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Related Party Transaction [Line Items]
Contributions from Dow and DowDuPont	$ 7,308	$ 88		$ 7,396	$ 288
Dow [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party			$ 41	42	112
Contributions from Dow and DowDuPont			$ 265	$ 88	$ 288