Retirement-Related Benefits - Nonpension Postretirement Cost (Details) - Nonpension Postretirement Plans - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
U.S.
Retirement-related plans cost
Service cost	$ 3	$ 4
Interest cost	33	38
Amortization of prior service costs/(credits)	(2)	(2)
Recognized actuarial losses	2	5
Total net periodic pension / nonpension (income)/cost of defined benefit plans	37	46
Non-U.S.
Retirement-related plans cost
Service cost	1	1
Interest cost	13	14
Expected return on plan assets	(1)	(2)
Amortization of prior service costs/(credits)	0	0
Recognized actuarial losses	1	2
Curtailments and settlements	0	0
Total net periodic pension / nonpension (income)/cost of defined benefit plans	$ 14	$ 16

Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan.

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Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) of defined benefit plan.

+ References

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Amount of expected return (loss) recognized in net periodic benefit (cost) credit, calculated based on expected long-term rate of return and market-related value of plan assets of defined benefit plan.

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Amount of cost recognized for passage of time related to defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)(2)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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Amount of net periodic benefit cost (credit) for defined benefit plan.

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Amount of gain (loss) recognized in net periodic benefit (cost) credit from settlement and curtailment.

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- Definition

Amount of cost for actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)(1)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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-Topic 715
-SubTopic 20
-Section 50
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-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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