Pension and Postretirement Plans (Reconciliation of Projected Benefit Obligations and Plan Assets) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Benefits \| United States
Change in Benefit Obligation
Benefit obligation at January 1	$ 2,881	$ 2,791
Service cost	132	127	$ 124
Interest cost	108	116	109
Actuarial loss (gain)	267	62
Benefits paid	(345)	(215)
Benefit obligation at December 31	3,043	2,881	2,791
Change in Fair Value of Plan Assets
Fair value of plan assets at January 1	2,274	2,023
Actual return on plan assets	399	136
Company contributions	423	330
Benefits paid	(345)	(215)
Fair value of plan assets at December 31	2,751	2,274	2,023
Funded Status at December 31	(292)	(607)
Pension Benefits \| Int’l.
Change in Benefit Obligation
Benefit obligation at January 1	1,055	912
Service cost	32	32	38
Interest cost	27	28	28
Plan participant contributions	2	3
Actuarial loss (gain)	(5)	237
Benefits paid	(20)	(19)
Curtailment gain		(31)
Foreign currency exchange rate change	118	(107)
Benefit obligation at December 31	1,209	1,055	912
Change in Fair Value of Plan Assets
Fair value of plan assets at January 1	796	742
Actual return on plan assets	71	148
Company contributions	35	40
Plan participant contributions	2	3
Benefits paid	(20)	(19)
Foreign currency exchange rate change	88	(118)
Fair value of plan assets at December 31	972	796	742
Funded Status at December 31	(237)	(259)
Other Benefits
Change in Benefit Obligation
Benefit obligation at January 1	225	219
Service cost	6	7	7
Interest cost	8	8	7
Plan participant contributions	3	2
Actuarial loss (gain)	6	(6)
Benefits paid	(16)	(13)
Acquisition of a business		8
Benefit obligation at December 31	232	225	$ 219
Change in Fair Value of Plan Assets
Company contributions	13	11
Plan participant contributions	3	2
Benefits paid	(16)	(13)
Funded Status at December 31	$ (232)	$ (225)

Amount of increase (decrease) in plan assets of defined benefit plan from actual return (loss) determined by change in fair value of plan assets adjusted for contributions, benefit payments, and other expenses.

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

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Amount of payment to participant of defined benefit plan which decreases benefit obligation. For pension plan, payment includes, but is not limited to, pension benefits and death benefits. For other postretirement plan, payment includes, but is not limited to, prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 60
-Section 50
-Paragraph 4
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- Definition

Amount of contributions received by defined benefit plan from participant which increase benefit obligation.

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Amount of increase in benefit obligation of defined benefit plan from business combination.

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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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No definition available.

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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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No definition available.

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Amount of contribution received by defined benefit plan from employer which increases plan assets.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Amount of (increase) decrease in benefit obligation of defined benefit plan from event reducing expected years of future service of present employees or eliminating accrual of benefits for some or all future services of present employees.

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- Definition

Fair value of assets that have been segregated and restricted to provide pension or postretirement benefits. Assets include, but are not limited to, stocks, bonds, other investments, earnings from investments, and contributions by the employer and employees.

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- Definition

Amount of foreign currency translation gain (loss) which (increases) decreases benefit obligation of defined benefit plan.

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- Definition

Amount of funded (unfunded) status of defined benefit plan, measured as difference between fair value of plan assets and benefit obligation. Includes, but is not limited to, overfunded (underfunded) status.

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

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- Definition

Amount of payment to participant under defined benefit plan which decreases plan assets. For pension plan, payment includes, but is not limited to, pension benefits and death benefits. For other postretirement plan, payment includes, but is not limited to, prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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-SubTopic 60
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6414203&loc=d3e39716-114964

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-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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Amount of contributions received by defined benefit plan from participant which increases plan assets.

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Amount of foreign currency translation gain (loss) which increases (decreases) plan assets of defined benefit plan.

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

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