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Pension and Other Postretirement Benefit Plans - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation		$ 22,800	$ 19,000
Employer contributions to defined contribution savings plans		$ 149	$ 136	$ 131
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Percentage of Company's pension investments categorized as Level 3 assets (as percent)		4.00%	5.00%
Pension Benefits | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		$ 860	$ 826
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		1,102	968	$ 1,114
Expected contributions to the pension plans and other postretirement benefit plans during next fiscal year		15
Other Postretirement Benefits | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		$ 0	$ 0
United States
Defined Benefit Plan Disclosure [Line Items]
Expected annual standard deviation in returns of the target portfolio which reflects both the equity allocation and the diversification benefits among the asset classes in which the portfolio invests (as percent)		10.00%
Expected rate of return on plan assets (as percent)		8.10%	8.20%	8.70%
United States | Minimum
Defined Benefit Plan Disclosure [Line Items]
Expected rate of return on plan assets (as percent)		7.70%
United States | Minimum | Forecast
Defined Benefit Plan Disclosure [Line Items]
Expected rate of return on plan assets (as percent)	7.00%
United States | Maximum
Defined Benefit Plan Disclosure [Line Items]
Expected rate of return on plan assets (as percent)		8.10%
United States | Maximum | Forecast
Defined Benefit Plan Disclosure [Line Items]
Expected rate of return on plan assets (as percent)	7.30%
United States | U.S. equities | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target allocation (as percent)		30.00%
United States | U.S. equities | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target allocation (as percent)		45.00%
United States | International equities | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target allocation (as percent)		15.00%
United States | International equities | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target allocation (as percent)		30.00%
United States | Fixed Income Investments | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target allocation (as percent)		35.00%
United States | Fixed Income Investments | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target allocation (as percent)		45.00%
United States | Cash And Other Investments | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target allocation (as percent)		5.00%
United States | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation		$ 12,800	$ 10,400
Fair value of plan assets		11,361	9,648	$ 10,896
Expected contributions to the pension plans and other postretirement benefit plans during next fiscal year		100
United States | Pension Benefits | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		9	13	15
International | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		10,163	$ 8,580	$ 9,339
Expected contributions to the pension plans and other postretirement benefit plans during next fiscal year		$ 150
Expected rate of return on plan assets (as percent)		4.90%	5.10%	5.10%
International | Pension Benefits | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		$ 851	$ 813	$ 473

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Company pension investments which are categorized as level three assets percentage.

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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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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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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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