Employee Benefit Plans (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
U.S.
Change in Plan Assets
Employer contributions	$ 728
Pension Benefits \| U.S.
Change in Benefit Obligation
Benefit obligation at January 1	13,271	$ 13,563
Service cost	489	494	$ 538
Interest cost	366	377	502
Plan participants' contributions	0	0
Plan amendments	0	0
Actuarial (gain) loss	1,168	903
Foreign currency exchange rate changes	0	0
Benefits paid	(1,714)	(2,066)
Divestitures	0	0
Benefit obligation at December 31	13,580	13,271	13,563
Change in Plan Assets
Fair value of plan assets at January 1	9,550	10,274
Actual return on plan assets	1,384	936
Foreign currency exchange rate changes	0	0
Employer contributions	728	406
Plan participants' contributions	0	0
Benefits paid	(1,714)	(2,066)
Divestitures	0	0
Fair value of plan assets at December 31	9,948	9,550	10,274
Funded status at December 31	(3,632)	(3,721)
Pension Benefits \| Int’l.
Change in Benefit Obligation
Benefit obligation at January 1	5,169	5,336
Service cost	151	159	185
Interest cost	219	261	277
Plan participants' contributions	4	5
Plan amendments	1	0
Actuarial (gain) loss	(37)	426
Foreign currency exchange rate changes	374	(524)
Benefits paid	(310)	(494)
Divestitures	(31)	0
Benefit obligation at December 31	5,540	5,169	5,336
Change in Plan Assets
Fair value of plan assets at January 1	4,174	4,109
Actual return on plan assets	319	642
Foreign currency exchange rate changes	358	(552)
Employer contributions	252	464
Plan participants' contributions	4	5
Benefits paid	(310)	(494)
Divestitures	(31)	0
Fair value of plan assets at December 31	4,766	4,174	4,109
Funded status at December 31	(774)	(995)
Other Benefits
Change in Benefit Obligation
Benefit obligation at January 1	2,549	3,324
Service cost	32	60	72
Interest cost	95	128	151
Plan participants' contributions	78	148
Plan amendments	0	(345)
Actuarial (gain) loss	266	(437)
Foreign currency exchange rate changes	10	8
Benefits paid	(229)	(337)
Divestitures	(13)	0
Benefit obligation at December 31	2,788	2,549	3,324
Change in Plan Assets
Fair value of plan assets at January 1	0	0
Actual return on plan assets	0	0
Foreign currency exchange rate changes	0	0
Employer contributions	151	189
Plan participants' contributions	78	148
Benefits paid	(229)	(337)
Divestitures	0	0
Fair value of plan assets at December 31	0	0	$ 0
Funded status at December 31	$ (2,788)	$ (2,549)

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

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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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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 decrease in benefit obligation of defined benefit plan from disposal or classification as held-for-sale.

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Amount of decrease in plan assets of defined benefit plan from disposal or classification as held-for-sale.

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

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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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Amount of increase (decrease) in benefit obligation of defined benefit plan from change in terms of existing plan or initiation of new plan.

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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.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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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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