Goodwill and Other Intangible Assets Other Intangible Assets (Details) - USD ($) $ in Millions		3 Months Ended
		Dec. 31, 2019	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2020
Intangible Assets [Line Items]
Definite-Lived Intangible Assets, Gross		$ 10,750			$ 12,599
Accumulated Amortization		(1,207)			(1,862)
Definite-Lived Intangible Assets, Net		9,543			10,737
Indefinite-lived Intangible Assets		1,881			10
Total Intangible Assets, Gross		12,631			12,609
Total intangible assets - net		11,424			10,747
IPR&D [Member]
Intangible Assets [Line Items]
Indefinite-lived Intangible Assets		10			10
Impairment of Intangible Assets, Indefinite-lived (Excluding Goodwill)		90	$ 54	$ 85
Impairment of Intangible Assets Indefinite lived Excluding Goodwill After Tax		69	$ 41	$ 66
Trademarks and Trade Names [Member]
Intangible Assets [Line Items]
Indefinite-lived Intangible Assets	[1]	1,871
Germplasm [Member]
Intangible Assets [Line Items]
Definite-Lived Intangible Assets, Gross	[2]	6,265			6,265
Accumulated Amortization	[2]	(63)			(317)
Definite-Lived Intangible Assets, Net	[2]	6,202			5,948
Customer-Related Intangible Assets [Member]
Intangible Assets [Line Items]
Definite-Lived Intangible Assets, Gross		1,977			1,984
Accumulated Amortization		(268)			(380)
Definite-Lived Intangible Assets, Net		1,709			1,604
Developed Technology [Member]
Intangible Assets [Line Items]
Definite-Lived Intangible Assets, Gross		1,463			1,451
Accumulated Amortization		(370)			(525)
Definite-Lived Intangible Assets, Net		1,093			926
Trademarks and Trade Names [Member]
Intangible Assets [Line Items]
Definite-Lived Intangible Assets, Gross	[1]	166			2,019
Accumulated Amortization	[1]	(86)			(99)
Definite-Lived Intangible Assets, Net	[1]	80			1,920
Favorable Supply Contract [Member]
Intangible Assets [Line Items]
Definite-Lived Intangible Assets, Gross		475			475
Accumulated Amortization		(207)			(302)
Definite-Lived Intangible Assets, Net		268			173
Other Intangible Assets [Member]
Intangible Assets [Line Items]
Definite-Lived Intangible Assets, Gross	[3]	404			405
Accumulated Amortization	[3]	(213)			(239)
Definite-Lived Intangible Assets, Net	[3]	$ 191			$ 166

[1] Beginning on October 1, 2020, the company changed its indefinite life assertion of its trade name asset to definite lived with a useful life of 25 years. This change is the result of the launch of BrevantTM seed in the retail channel in the U.S. Prior to changing the useful life of the trade name asset, the company tested the asset for impairment under ASC 350 - Intangibles, Goodwill and Other, concluding the asset was not impaired.

[2] Beginning on October, 1, 2019, the company changed its indefinite life assertion of germplasm assets to definite lived with a useful life of 25 years. The change is a result of a more focused development effort of new seed products coupled with an intent to out license select germplasm on a nonexclusive basis. Prior to changing the useful life of the germplasm assets, the company tested the assets for impairment under ASC 350 - Intangibles, Goodwill and Other, concluding the assets were not impaired. The increase in accumulated amortization for the year ended December 31, 2020 when compared to the year ended December 31, 2019 is due to 2020 including a full year of amortization of germplasm assets

[3] Primarily consists of sales and farmer networks, marketing and manufacturing alliances and noncompetition agreements.