Financial Instruments - Pre-Tax Gains and Losses of Derivative and Non-Derivative Instruments Designated as Hedges (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Mar. 31, 2018	Apr. 01, 2017	Mar. 31, 2018	Apr. 01, 2017
Cash flow hedges
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(Losses) recognized in OCI - effective portion	$ 37	$ (315)	$ 191	$ 1,419
Gains/(Losses) reclassified from AOCI into net income - effective portion	289	1,342	166	830
Cash flow hedges \| Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(Losses) recognized in OCI - effective portion	37	(317)	190	1,410
Gains/(Losses) reclassified from AOCI into net income - effective portion	287	1,344	163	833
Cash flow hedges \| Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(Losses) recognized in OCI - effective portion	0	2	1	9
Gains/(Losses) reclassified from AOCI into net income - effective portion	2	(2)	3	(3)
Net investment hedges \| Foreign currency debt
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(Losses) recognized in OCI - effective portion	(33)	(85)	(31)	37
Fair value hedges \| Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(Losses) on derivative instruments	(674)	(50)	(948)	(922)
Gains/(Losses) related to hedged fixed-rate debt	$ 674	$ 50	$ 948	$ 922

Amount of the increase (decrease) in fair value of the hedged item in a fair value hedge recognized in the income statement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 25
-Section 50
-Paragraph 1
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=6886632&loc=d3e76258-113986

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- Definition

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5618551-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (a),(c),(d),(e)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

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The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4D
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624177-113959

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- Definition

The effective portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments that was recognized in other comprehensive income during the current period.

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