Percentage-of-Completion Contracts (Detail) - USD ($) $ in Millions	Mar. 31, 2018	Sep. 30, 2017
Disclosure Percentage Of Completion Contracts Additional Information [Abstract]
Costs and earnings in excess of billings related to contracts	$ 1,065	$ 908
Billing in excess of costs and earnings on uncompleted contracts	$ 565	$ 451

Amount of receivable reflecting the cost incurred on uncompleted contracts in excess of related billings.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 912
-SubTopic 310
-Section 45
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-URI http://asc.fasb.org/extlink&oid=68054760&loc=d3e55302-109406

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Subparagraph (SX 210.5-02(3)(c)(4))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Topic 605
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-Section 45
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-URI http://asc.fasb.org/extlink&oid=68068069&loc=d3e57807-111642

Name:	us-gaap_CostsInExcessOfBillingsOnUncompletedContractsOrPrograms
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant