Pension and Postretirement Benefit Plans and Defined Contribution Plans - Obligations and Funded Status (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Postretirement Benefits Plan [Member]
Change in benefit obligation
Benefit obligation, beginning	$ 1,870	$ 2,028
Service cost	37	39	$ 42
Interest cost	75	72	90
Employee contributions	84	102
Plan amendments	(56)	2
Changes in actuarial assumptions and other	(87)	(122)
Foreign exchange impact	(1)	(4)
Acquisitions/divestitures/other, net	(36)	0
Curtailments	0	(1)
Settlements	0	0
Special termination benefits	2	2
Benefits paid	(221)	(249)
Benefit obligation, ending	1,667	1,870	2,028
Change in plan assets
Fair value of plan assets, beginning	469	494
Actual gain/(loss) on plan assets	50	(22)
Company contributions	137	145
Employee contributions	84	102
Foreign exchange impact	0	0
Acquisitions/divestitures, net	0	0
Settlements	0	0
Benefits paid	(221)	(249)
Fair value of plan assets, ending	519	469	494
Funded status—Plan assets less than benefit obligation	(1,148)	(1,401)
Foreign Plan [Member] \| Pension Plan [Member]
Change in benefit obligation
Benefit obligation, beginning	9,952	10,607
Service cost	125	136	171
Interest cost	215	212	204
Employee contributions	7	7
Plan amendments	18	29
Changes in actuarial assumptions and other	1,224	(169)
Foreign exchange impact	(33)	(457)
Acquisitions/divestitures/other, net	(55)	(2)
Curtailments	(2)	(3)
Settlements	(34)	(34)
Special termination benefits	0	0
Benefits paid	(360)	(373)
Benefit obligation, ending	11,059	9,952	10,607
Change in plan assets
Fair value of plan assets, beginning	8,215	8,863
Actual gain/(loss) on plan assets	873	(77)
Company contributions	230	209
Employee contributions	7	7
Foreign exchange impact	42	(380)
Acquisitions/divestitures, net	(16)	0
Settlements	(34)	(34)
Benefits paid	(360)	(373)
Fair value of plan assets, ending	8,956	8,215	8,863
Funded status—Plan assets less than benefit obligation	(2,103)	(1,738)
Defined benefit plan, accumulated benefit obligation	10,600	9,500
Qualified Plan [Member] \| United States [Member] \| Pension Plan [Member]
Change in benefit obligation
Benefit obligation, beginning	15,141	16,702
Service cost	0	0	269
Interest cost	629	598	634
Employee contributions	0	0
Plan amendments	0	(22)
Changes in actuarial assumptions and other	2,001	(1,219)
Foreign exchange impact	0	0
Acquisitions/divestitures/other, net	(4)	0
Curtailments	0	11
Settlements	(692)	(391)
Special termination benefits	4	6
Benefits paid	(544)	(546)
Benefit obligation, ending	16,535	15,141	16,702
Change in plan assets
Fair value of plan assets, beginning	13,051	14,284
Actual gain/(loss) on plan assets	2,760	(796)
Company contributions	11	500
Employee contributions	0	0
Foreign exchange impact	0	0
Acquisitions/divestitures, net	0
Settlements	(692)	(391)
Benefits paid	(544)	(546)
Fair value of plan assets, ending	14,586	13,051	14,284
Funded status—Plan assets less than benefit obligation	(1,949)	(2,089)
Nonqualified Plan [Member] \| United States [Member] \| U.S. Supplemental (Non-Qualified) Pension Plans [Member]
Change in benefit obligation
Benefit obligation, beginning	1,280	1,495
Service cost	0	0	24
Interest cost	47	55	54
Employee contributions	0	0
Plan amendments	0	0
Changes in actuarial assumptions and other	152	(152)
Foreign exchange impact	0	0
Acquisitions/divestitures/other, net	(1)	0
Curtailments	0	1
Settlements	(70)	(72)
Special termination benefits	17	10
Benefits paid	(74)	(58)
Benefit obligation, ending	1,351	1,280	1,495
Change in plan assets
Fair value of plan assets, beginning	0	0
Company contributions	144	129
Employee contributions	0	0
Foreign exchange impact	0	0
Settlements	(70)	(72)
Benefits paid	(74)	(58)
Fair value of plan assets, ending	0	0	$ 0
Funded status—Plan assets less than benefit obligation	$ (1,351)	$ (1,280)

Defined Benefit Plan, Business Combinations, Acquisitions and Divestitures, Benefit Obligation

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Defined Benefit Plan, Business Combinations, Acquisitions and Divestitures, Plan Assets

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Amount of actuarial present value of benefits attributed to employee service rendered, excluding assumptions about future compensation level.

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

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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 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 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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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 increase in benefit obligation for benefits provided to employees payable from defined benefit plan or payable upon retirement.

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