Pension and Other Postretirement Benefit Plans - Obligation and Funded Status (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Other Postretirement Benefits
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	$ 968	$ 1,114
Actual return on plan assets	203	(72)
Company contributions	14	6
Effects of exchange rate changes	0	0
Benefits paid	(104)	(80)
Settlements	0	0
Other	21	0
Fair value of plan assets December 31	1,102	968	$ 1,114
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation January 1	1,615	1,922
Service cost	48	57	57
Interest cost	69	69	81
Actuarial (gains) losses	21	(341)
Benefits paid	(104)	(80)
Effects of exchange rate changes	1	(6)
Plan amendments	0	(9)
Curtailments	0	0
Termination benefits	5	3	8
Settlements	0	0
Other	18	0
Benefit obligation December 31	1,673	1,615	1,922
Funded status December 31	(571)	(647)
Recognized as:
Other Assets	0	0
Accrued and other current liabilities	(10)	(10)
Other Noncurrent Liabilities	(561)	(637)
United States \| Pension Benefits
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	9,648	10,896
Actual return on plan assets	2,165	(810)
Company contributions	130	378
Effects of exchange rate changes	0	0
Benefits paid	(582)	(772)
Settlements	0	(44)
Other	0	0
Fair value of plan assets December 31	11,361	9,648	10,896
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation January 1	10,620	11,904
Service cost	293	326	312
Interest cost	458	432	454
Actuarial (gains) losses	2,165	(1,258)
Benefits paid	(582)	(772)
Effects of exchange rate changes	0	0
Plan amendments	0	0
Curtailments	18	13
Termination benefits	31	19	44
Settlements	0	(44)
Other	0	0
Benefit obligation December 31	13,003	10,620	11,904
Funded status December 31	(1,642)	(972)
Recognized as:
Other Assets	0	0
Accrued and other current liabilities	(92)	(47)
Other Noncurrent Liabilities	(1,550)	(925)
International \| Pension Benefits
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	8,580	9,339
Actual return on plan assets	1,505	(289)
Company contributions	262	167
Effects of exchange rate changes	31	(352)
Benefits paid	(230)	(202)
Settlements	(12)	(106)
Other	27	23
Fair value of plan assets December 31	10,163	8,580	9,339
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation January 1	9,083	9,483
Service cost	238	238	252
Interest cost	177	178	172
Actuarial (gains) losses	1,313	(154)
Benefits paid	(230)	(202)
Effects of exchange rate changes	4	(387)
Plan amendments	1	10
Curtailments	3	(2)
Termination benefits	8	2	4
Settlements	(12)	(106)
Other	27	23
Benefit obligation December 31	10,612	9,083	$ 9,483
Funded status December 31	(449)	(503)
Recognized as:
Other Assets	837	659
Accrued and other current liabilities	(18)	(14)
Other Noncurrent Liabilities	$ (1,268)	$ (1,148)

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

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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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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 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 increase (decrease) in benefit obligation of defined benefit plan from change, classified as other.

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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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