Employee Benefit Plans - Amounts recognized in Balance Sheet And Assumptions (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Amounts Recognized in the Consolidated Balance Sheet
Noncurrent liabilities	$ (1,697)	$ (1,781)
Pension Plans Defined Benefit [Member] \| US
Amounts Recognized in the Consolidated Balance Sheet
Noncurrent assets	0	0
Current liabilities	(56)	(21)
Noncurrent liabilities	(722)	(707)
Total recognized	$ (778)	$ (728)
Weighted-Average Assumptions Used to Determine Benefit Obligations at December 31
Discount rate	2.30%	3.25%
Rate of compensation increase	4.00%	4.00%
Interest crediting rate for applicable benefits	2.10%	4.10%
Weighted-Average Assumptions Used to Determine Net Periodic Benefit Cost for Years Ended December 31
Discount rate	3.05%	3.95%
Expected return on plan assets	5.80%	5.80%
Rate of compensation increase	4.00%	4.00%
Interest crediting rate for applicable benefits	4.10%	4.35%
Before-tax amounts unrecognized in net periodic postretirement benefit cost
Unrecognized net actuarial loss (gain)	$ 467	$ 479
Unrecognized prior service cost (credit)	0	0
Pension Plans Defined Benefit [Member] \| Foreign Pension Plans, Defined Benefit [Member]
Amounts Recognized in the Consolidated Balance Sheet
Noncurrent assets	746	765
Current liabilities	(11)	(6)
Noncurrent liabilities	(345)	(333)
Total recognized	$ 390	$ 426
Weighted-Average Assumptions Used to Determine Benefit Obligations at December 31
Discount rate	1.80%	2.35%
Rate of compensation increase	3.10%	3.35%
Interest crediting rate for applicable benefits	0.00%	0.00%
Weighted-Average Assumptions Used to Determine Net Periodic Benefit Cost for Years Ended December 31
Discount rate	2.35%	2.90%
Expected return on plan assets	3.60%	4.10%
Rate of compensation increase	3.35%	3.65%
Interest crediting rate for applicable benefits	0.00%	0.00%
Before-tax amounts unrecognized in net periodic postretirement benefit cost
Unrecognized net actuarial loss (gain)	$ 326	$ 227
Unrecognized prior service cost (credit)	0	(2)
Other Postretirement Benefit Plans, Defined Benefit [Member]
Amounts Recognized in the Consolidated Balance Sheet
Noncurrent assets	0	0
Current liabilities	(39)	(42)
Noncurrent liabilities	(131)	(174)
Total recognized	$ (170)	$ (216)
Weighted-Average Assumptions Used to Determine Benefit Obligations at December 31
Discount rate	2.15%	3.10%
Weighted-Average Assumptions Used to Determine Net Periodic Benefit Cost for Years Ended December 31
Discount rate	3.10%	4.05%
Before-tax amounts unrecognized in net periodic postretirement benefit cost
Unrecognized net actuarial loss (gain)	$ 14	$ 8
Unrecognized prior service cost (credit)	$ (182)	$ (183)

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Amount, before tax, of accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.

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Amount, before tax, of accumulated other comprehensive (income) loss for cost (credit) of benefit change attributable to participants' prior service from plan amendment or plan initiation of defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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Amount of asset (liability), recognized in statement of financial position, for defined benefit pension and other postretirement plans.

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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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Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan.

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Weighted average rate increase of compensation, used to determine benefit obligation of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan.

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Weighted-average interest crediting rate used to determine benefit obligation of defined benefit plan. Plan includes, but is not limited to, cash balance and other defined benefit plans with promised interest crediting rate.

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Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost of defined benefit plan.

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Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan.

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Weighted average rate of compensation increase used to determine net periodic benefit cost of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan.

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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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