Pension and Other Postretirement Benefit Plans - Obligation and Funded Status (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Postretirement Benefits
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	$ 1,019	$ 1,913
Actual return on plan assets	161	138
Company contributions, net	(4)	68
Effects of exchange rate changes	0	0
Benefits paid	(62)	(108)
Settlements	0	0
Assets no longer restricted to the payment of postretirement benefits	0	(992)
Other	0	0
Fair value of plan assets December 31	1,114	1,019	$ 1,913
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation January 1	1,922	1,810
Service cost	57	54	80
Interest cost	81	82	110
Actuarial losses (gains)	(87)	77
Benefits paid	(62)	(108)
Effects of exchange rate changes	3	2
Plan amendments	0	0
Curtailments	0	1
Termination benefits	8	4	7
Settlements	0	0
Other	0	0
Benefit obligation December 31	1,922	1,922	1,810
Funded status December 31	(808)	(903)
Recognized as:
Other assets	0	0
Accrued and other current liabilities	(11)	(11)
Other noncurrent liabilities	(797)	(892)
United States \| Pension Plan
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	9,766	9,266
Actual return on plan assets	1,723	941
Company contributions, net	58	63
Effects of exchange rate changes	0	0
Benefits paid	(651)	(504)
Settlements	0	0
Assets no longer restricted to the payment of postretirement benefits	0	0
Other	0	0
Fair value of plan assets December 31	10,896	9,766	9,266
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation January 1	10,849	9,723
Service cost	312	282	307
Interest cost	454	456	434
Actuarial losses (gains)	881	854
Benefits paid	(651)	(504)
Effects of exchange rate changes	0	0
Plan amendments	0	0
Curtailments	15	15
Termination benefits	44	23	22
Settlements	0	0
Other	0	0
Benefit obligation December 31	11,904	10,849	9,723
Funded status December 31	(1,008)	(1,083)
Recognized as:
Other assets	0	0
Accrued and other current liabilities	(59)	(50)
Other noncurrent liabilities	(949)	(1,033)
International \| Pension Plan
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	7,794	7,204
Actual return on plan assets	677	898
Company contributions, net	226	424
Effects of exchange rate changes	843	(546)
Benefits paid	(198)	(193)
Settlements	(17)	(21)
Assets no longer restricted to the payment of postretirement benefits	0	0
Other	14	28
Fair value of plan assets December 31	9,339	7,794	7,204
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation January 1	8,372	7,733
Service cost	252	238	251
Interest cost	172	204	206
Actuarial losses (gains)	(7)	938
Benefits paid	(198)	(193)
Effects of exchange rate changes	916	(576)
Plan amendments	(22)	0
Curtailments	(3)	(15)
Termination benefits	4	4	1
Settlements	(17)	(21)
Other	14	60
Benefit obligation December 31	9,483	8,372	$ 7,733
Funded status December 31	(144)	(578)
Recognized as:
Other assets	828	451
Accrued and other current liabilities	(17)	(7)
Other noncurrent liabilities	$ (955)	$ (1,022)

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 increase (decrease) in plan assets of defined benefit plan from assets transferred into (from) 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.

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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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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, 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 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 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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