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Pension and Other Postretirement Benefit Plans - Summary of Changes in Fair Value of Company's Level 3 Pension Plan Assets (Details) - Pension Plan - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
United States
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance January 1	$ 4,542
Actual return on plan assets:
Balance December 31	5,189	$ 4,542
United States | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance January 1	18	23
Actual return on plan assets:
Relating to assets still held at December 31	(2)	(3)
Relating to assets sold during the year	4	4
Purchases and sales, net	(5)	(6)
Balance December 31	15	18
United States | Significant Unobservable Inputs (Level 3) | Insurance Contracts
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance January 1	0	0
Actual return on plan assets:
Relating to assets still held at December 31	0	0
Relating to assets sold during the year	0	0
Purchases and sales, net	0	0
Balance December 31	0	0
United States | Significant Unobservable Inputs (Level 3) | Real Estate
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance January 1	0	0
Actual return on plan assets:
Relating to assets still held at December 31	0	0
Relating to assets sold during the year	0	0
Purchases and sales, net	0	0
Balance December 31	0	0
United States | Significant Unobservable Inputs (Level 3) | Other
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance January 1	18	23
Actual return on plan assets:
Relating to assets still held at December 31	(2)	(3)
Relating to assets sold during the year	4	4
Purchases and sales, net	(5)	(6)
Balance December 31	15	18
International
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance January 1	7,006
Actual return on plan assets:
Balance December 31	8,537	7,006
International | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance January 1	417	400
Actual return on plan assets:
Relating to assets still held at December 31	52	(8)
Purchases and sales, net	3	(1)
Transfers into Level 3	1	26
Balance December 31	473	417
International | Significant Unobservable Inputs (Level 3) | Insurance Contracts
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance January 1	412	393
Actual return on plan assets:
Relating to assets still held at December 31	52	(9)
Purchases and sales, net	5	2
Transfers into Level 3	1	26
Balance December 31	470	412
International | Significant Unobservable Inputs (Level 3) | Real Estate
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance January 1	4	5
Actual return on plan assets:
Relating to assets still held at December 31	0	1
Purchases and sales, net	(2)	(2)
Transfers into Level 3	0	0
Balance December 31	2	4
International | Significant Unobservable Inputs (Level 3) | Other
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance January 1	1	2
Actual return on plan assets:
Relating to assets still held at December 31	0	0
Purchases and sales, net	0	(1)
Transfers into Level 3	0	0
Balance December 31	$ 1	$ 1

X

- Definition

Defined Benefit Plan, Fair Value of Plan Assets, Excluding Net Asset Value Investments

+ References

No definition available.

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- References

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- Definition

Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets sold.

+ 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 (d)(5)(iv)(02)(A)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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- Definition

Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets still held.

+ 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 (d)(5)(iv)(02)(A)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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- Definition

Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from purchases, sales and settlements.

+ 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 (d)(5)(iv)(02)(B)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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- Definition

Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan, for assets transferred into (out of) Level 3 of fair value hierarchy. Includes, but is not limited to, transfer due to change in observability of significant inputs.

+ 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 (d)(5)(iv)(02)(C)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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