Pension and Other Postretirement Benefit Plans - Obligation and Funded Status (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other Postretirement Benefits
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	$ 1,114	$ 1,019
Actual return on plan assets	(72)	161
Company contributions, net	6	(4)
Effects of exchange rate changes	0	0
Benefits paid	(80)	(62)
Settlements	0	0
Other	0	0
Fair value of plan assets December 31	968	1,114	$ 1,019
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation January 1	1,922	1,922
Service cost	57	57	54
Interest cost	69	81	82
Actuarial (gains) losses	(341)	(87)
Benefits paid	(80)	(62)
Effects of exchange rate changes	(6)	3
Plan amendments	(9)	0
Curtailments	0	0
Termination benefits	3	8	4
Settlements	0	0
Other	0	0
Benefit obligation December 31	1,615	1,922	1,922
Funded status December 31	(647)	(808)
Recognized as:
Other assets	0	0
Accrued and other current liabilities	(10)	(11)
Other noncurrent liabilities	(637)	(797)
United States \| Pension Benefits
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	10,896	9,766
Actual return on plan assets	(810)	1,723
Company contributions, net	378	58
Effects of exchange rate changes	0	0
Benefits paid	(772)	(651)
Settlements	(44)	0
Other	0	0
Fair value of plan assets December 31	9,648	10,896	9,766
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation January 1	11,904	10,849
Service cost	326	312	282
Interest cost	432	454	456
Actuarial (gains) losses	(1,258)	881
Benefits paid	(772)	(651)
Effects of exchange rate changes	0	0
Plan amendments	0	0
Curtailments	13	15
Termination benefits	19	44	23
Settlements	(44)	0
Other	0	0
Benefit obligation December 31	10,620	11,904	10,849
Funded status December 31	(972)	(1,008)
Recognized as:
Other assets	0	0
Accrued and other current liabilities	(47)	(59)
Other noncurrent liabilities	(925)	(949)
International \| Pension Benefits
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	9,339	7,794
Actual return on plan assets	(289)	677
Company contributions, net	167	226
Effects of exchange rate changes	(352)	843
Benefits paid	(202)	(198)
Settlements	(106)	(17)
Other	23	14
Fair value of plan assets December 31	8,580	9,339	7,794
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation January 1	9,483	8,372
Service cost	238	252	238
Interest cost	178	172	204
Actuarial (gains) losses	(154)	(7)
Benefits paid	(202)	(198)
Effects of exchange rate changes	(387)	916
Plan amendments	10	(22)
Curtailments	(2)	(3)
Termination benefits	2	4	4
Settlements	(106)	(17)
Other	23	14
Benefit obligation December 31	9,083	9,483	$ 8,372
Funded status December 31	(503)	(144)
Recognized as:
Other assets	659	828
Accrued and other current liabilities	(14)	(17)
Other noncurrent liabilities	$ (1,148)	$ (955)

Changes in plan assets, not otherwise separately disclosed in the financial statements.

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Defined Benefit Plan, Plan Assets, Contributions by Employer, Net

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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 asset, recognized in statement of financial position, for overfunded defined benefit pension and other postretirement plans.

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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.

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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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Amount of cost of providing special or contractual termination benefits payable from defined benefit plan.

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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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Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee.

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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, classified as other.

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

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Amount of (increase) decrease to benefit obligation of defined benefit plan from irrevocable action relieving primary responsibility for benefit obligation and eliminating risk for obligation and assets used to effect settlement. Includes, but is not limited to, lump-sum cash payment to participant in exchange for right to receive specified benefits, purchase of nonparticipating annuity contract and change from remeasurement.

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Amount of payment, which decreases plan assets of defined benefit plan, for irrevocable action relieving primary responsibility for benefit obligation and eliminating risk for obligation and assets used to effect settlement. Transaction constituting settlement includes, but is not limited to, making lump-sum cash payment to participant in exchange for their rights to receive specified benefits and purchasing nonparticipating annuity contract.

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Amount of liability, recognized in statement of financial position, for defined benefit pension and other postretirement plans, classified as current.

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Amount of liability, recognized in statement of financial position, for defined benefit pension and other postretirement plans, classified as noncurrent.

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