Restructuring and Impairment Costs (Details) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Mar. 31, 2019 USD ($) employee	Mar. 31, 2018 USD ($)	Mar. 31, 2019 USD ($) employee plant	Mar. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)
Restructuring Cost and Reserve [Line Items]
Underspend					$ 7
Restructuring and impairment costs	$ 113	$ 315	$ 144	$ 315
Number of positions eliminated to date | employee	7,300		7,300
Number of positions eliminated | employee			5,000
Number of plants expected to close | plant			15
Number of plants closed | plant			11
Fixed asset impairment charges	$ 66
Goodwill impairment charge	299	$ 299
2019 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs, gross			$ 80
Underspend			(8)
2018 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs, gross					71
Underspend			(2)
2018 Restructuring Plan | Employee Severance and Termination Benefits
Restructuring Cost and Reserve [Line Items]
Underspend			(2)
2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs						$ 46
2017 Restructuring Plan | Employee Severance and Termination Benefits
Restructuring Cost and Reserve [Line Items]
Underspend					6
2016 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Underspend					20
Restructuring and impairment costs							$ 332
2016 Restructuring Plan | Employee Severance and Termination Benefits
Restructuring Cost and Reserve [Line Items]
Underspend					20
Fixed Assets
Restructuring Cost and Reserve [Line Items]
Fixed asset impairment charges	62
Customer relationships
Restructuring Cost and Reserve [Line Items]
Fixed asset impairment charges	4
Asia | 2019 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs, gross			6
Asia | 2018 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs, gross					10
Asia | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs						5
Asia | 2016 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs							2
EMEA
Restructuring Cost and Reserve [Line Items]
Fixed asset impairment charges	55
EMEA | 2019 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs, gross			61
EMEA | 2018 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs, gross					52
EMEA | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs						34
EMEA | 2016 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs							298
Americas
Restructuring Cost and Reserve [Line Items]
Fixed asset impairment charges	$ 11
Americas | 2019 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs, gross			$ 13
Americas | 2018 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs, gross					$ 9
Americas | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs						$ 7
Americas | 2016 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs							$ 32