Segment Information - Financial Information Related to Company's Reportable Segments (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Net sales	$ 7,475		$ 7,267		$ 14,910	$ 14,353
Segment EBITA	929		956		1,969	1,780
Corporate expenses	(159)		(240)		(293)	(433)
Amortization of intangible assets	(94)		(126)		(188)	(275)
Restructuring and impairment costs	0	$ (158)	(99)	$ (78)	(158)	(177)
Net mark-to-market adjustments on pension plans	0		18	$ 117	0	135
Net financing charges	(115)		(116)		(231)	(252)
Income from continuing operations before income taxes	561		393		1,099	778
Power Solutions
Segment Reporting Information [Line Items]
Net sales	1,845		1,696		3,975	3,596
Segment EBITA	314		303		698	692
Building Technologies & Solutions
Segment Reporting Information [Line Items]
Net sales	5,630		5,571		10,935	10,757
Segment EBITA	615		653		1,271	1,088
Building Technologies & Solutions \| Building Solutions North America
Segment Reporting Information [Line Items]
Net sales	2,097		2,097		4,109	4,039
Segment EBITA	239		255		466	451
Building Technologies & Solutions \| Building Solutions EMEA/LA
Segment Reporting Information [Line Items]
Net sales	907		898		1,822	1,773
Segment EBITA	77		89		146	138
Building Technologies & Solutions \| Building Solutions Asia Pacific
Segment Reporting Information [Line Items]
Net sales	586		562		1,183	1,137
Segment EBITA	71		67		145	130
Building Technologies & Solutions \| Global Products
Segment Reporting Information [Line Items]
Net sales	2,040		2,014		3,821	3,808
Segment EBITA	$ 228		$ 242		$ 514	$ 369

General expenses recorded at the Corporate segment.

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Net financing charges includes interest expense, interest income, bank fees and amortization of debt issuance costs.

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Amount of income or loss from continuing operations before income taxes and noncontrolling interests, excluding general corporate expenses, intangible asset amortization, net financing charges, significant restructuring and impairment costs, and net mark-to-market adjustments on pension and postretirement plans.

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The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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Amount of gain (loss) from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan.

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Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

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Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation.

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Total revenue from sale of goods and services rendered during the reporting period, in the normal course of business, reduced by sales returns and allowances, and sales discounts.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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