The end date of the period reflected on the cover page if a periodic report. For all other reports and registration statements containing historical data, it is the date up through which that historical data is presented. If there is no historical data in the report, use the filing date. The format of the date is CCYY-MM-DD.

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Summary of Significant Accounting Policies Accounting Policies (Details)	3 Months Ended		12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2019 USD ($) Segment $ / shares	Sep. 30, 2018 USD ($) $ / shares	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2019 USD ($)
Financial Statement Details [Line Items]
Accounts receivable - net			$ 5,770,000,000	$ 5,622,000,000
Inventories			1,814,000,000	1,819,000,000
Assets held for sale			98,000,000	3,015,000,000
Other current assets			$ 1,906,000,000	1,182,000,000
Cash in escrow related to Adient debt						$ 2,000,000,000.0
Deferred tax asset from stock options exercised and restricted stock vestings		$ 179,000,000
Number of Countries in which Entity Operates			150
Maturity period to be considered cash equivalents			3 months
Document Period End Date			Sep. 30, 2019
Restricted Cash and Cash Equivalents			$ 16,000,000	15,000,000
Restricted Cash and Investments, Current				6,000,000
Restricted Cash and Cash Equivalents, Noncurrent				9,000,000
Liability for Asbestos and Environmental Claims, Gross			$ 507,000,000	550,000,000
Pooled subscriber assets and related deferred revenue, useful life			12 years
Non-pooled subscriber assets and related deferred revenue, useful life			15 years
Standard chargeback period from dealer for monitoring service cancellations			6 months
Non-standard chargeback period from dealer for monitoring service cancellations			12 months
Research and Development Expense			$ 319,000,000	310,000,000	$ 307,000,000
Foreign currency transaction gains (losses)			$ (10,000,000)	$ 1,000,000	60,000,000
Number of reportable segments \| Segment			4
Proceeds from Issuance of Unsecured Debt						$ 2,000,000,000.0
Ordinary shares, par value \| $ / shares			$ 0.01	$ 0.01
Net sales			$ 23,968,000,000	$ 23,400,000,000	22,835,000,000
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest			1,056,000,000	1,546,000,000	1,151,000,000
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest			4,598,000,000	1,034,000,000	990,000,000
Property, plant and equipment - net			3,348,000,000	3,300,000,000	$ 3,341,000,000
Other noncurrent assets			1,823,000,000	3,070,000,000
Deferred revenue			1,407,000,000	1,326,000,000
Disposal Group, Including Discontinued Operation, Liabilities			44,000,000	1,791,000,000
Retained earnings			$ 4,827,000,000	$ 6,604,000,000
Minimum
Financial Statement Details [Line Items]
Estimated useful life of dealer intangible assets			12 years
Maximum
Financial Statement Details [Line Items]
Estimated useful life of dealer intangible assets			15 years
Building And Improvements \| Minimum
Financial Statement Details [Line Items]
Estimated useful lives			3 years
Building And Improvements \| Maximum
Financial Statement Details [Line Items]
Estimated useful lives			40 years
Machinery and Equipment \| Minimum
Financial Statement Details [Line Items]
Estimated useful lives			3 years
Machinery and Equipment \| Maximum
Financial Statement Details [Line Items]
Estimated useful lives			15 years
Accounting Standards Update 2016-16 [Member]
Financial Statement Details [Line Items]
Cumulative Effect on Retained Earnings, Net of Tax			$ (546,000,000)
Accounting Standards Update 2016-01 [Member]
Financial Statement Details [Line Items]
Cumulative Effect on Retained Earnings, Net of Tax			0
Accounting Standards Update 2014-09 [Member]
Financial Statement Details [Line Items]
Cumulative Effect on Retained Earnings, Net of Tax			(45,000,000)
Accounting Standards Update 2016-02 [Member]
Financial Statement Details [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification			0.03
Retained Earnings \| Accounting Standards Update 2016-16 [Member]
Financial Statement Details [Line Items]
Cumulative Effect on Retained Earnings, Net of Tax			(546,000,000)
Retained Earnings \| Accounting Standards Update 2016-01 [Member]
Financial Statement Details [Line Items]
Cumulative Effect on Retained Earnings, Net of Tax	$ 8,000,000		8,000,000
Retained Earnings \| Accounting Standards Update 2014-09 [Member]
Financial Statement Details [Line Items]
Cumulative Effect on Retained Earnings, Net of Tax			(45,000,000)
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Financial Statement Details [Line Items]
Accounts receivable - net			(32,000,000)
Inventories			(14,000,000)
Other current assets			(25,000,000)
Property, plant and equipment - net			40,000,000
Other noncurrent assets			29,000,000
Deferred revenue			9,000,000
Retained earnings			(11,000,000)
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] \| Accounting Standards Update 2014-09 [Member]
Financial Statement Details [Line Items]
Net sales			3,000,000
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest			1,000,000
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Financial Statement Details [Line Items]
Accounts receivable - net			5,802,000,000
Inventories			1,828,000,000
Other current assets			1,931,000,000
Property, plant and equipment - net			3,308,000,000
Other noncurrent assets			1,794,000,000
Deferred revenue			1,398,000,000
Retained earnings			4,838,000,000
Power Solutions \| Difference between Revenue Guidance in Effect before and after Topic 606 [Member] \| Accounting Standards Update 2014-09 [Member]
Financial Statement Details [Line Items]
Disposal Group, Including Discontinued Operation, Revenue			667,000,000
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest			$ 26,000,000
Power Solutions
Financial Statement Details [Line Items]
Disposal Group, Including Discontinued Operation, Consideration							$ 13,200,000,000
Disposal Group, Discontinued Operations, Consideration, net							$ 11,600,000,000