Pension and Other Postretirement Benefit Plans - Summary of Changes in Fair Value of Company's Level 3 Pension Plan Assets (Details) - Pension Benefits - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Significant Unobservable Inputs (Level 3)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	$ 488
Actual return on plan assets:
Fair value of plan assets December 31	826	$ 488
United States
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	10,896	9,766
Actual return on plan assets:
Fair value of plan assets December 31	9,648	10,896
United States \| Significant Unobservable Inputs (Level 3)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	15	18
Actual return on plan assets:
Relating to assets still held at December 31	(3)	(2)
Relating to assets sold during the year	4	4
Purchases and sales, net	(3)	(5)
Fair value of plan assets December 31	13	15
United States \| Significant Unobservable Inputs (Level 3) \| Insurance Contracts
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	0	0
Actual return on plan assets:
Relating to assets still held at December 31	0	0
Relating to assets sold during the year	0	0
Purchases and sales, net	0	0
Fair value of plan assets December 31	0	0
United States \| Significant Unobservable Inputs (Level 3) \| Real Estate
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	0	0
Actual return on plan assets:
Relating to assets still held at December 31	0	0
Relating to assets sold during the year	0	0
Purchases and sales, net	0	0
Fair value of plan assets December 31	0	0
United States \| Significant Unobservable Inputs (Level 3) \| Other
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	15	18
Actual return on plan assets:
Relating to assets still held at December 31	(3)	(2)
Relating to assets sold during the year	4	4
Purchases and sales, net	(3)	(5)
Fair value of plan assets December 31	13	15
International
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	9,339	7,794
Actual return on plan assets:
Fair value of plan assets December 31	8,580	9,339
International \| Significant Unobservable Inputs (Level 3)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	473	417
Actual return on plan assets:
Relating to assets still held at December 31	(32)	52
Purchases and sales, net	379	3
Transfers into Level 3	(7)	1
Fair value of plan assets December 31	813	473
International \| Significant Unobservable Inputs (Level 3) \| Insurance Contracts
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	470	412
Actual return on plan assets:
Relating to assets still held at December 31	(32)	52
Purchases and sales, net	380	5
Transfers into Level 3	(7)	1
Fair value of plan assets December 31	811	470
International \| Significant Unobservable Inputs (Level 3) \| Real Estate
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	2	4
Actual return on plan assets:
Relating to assets still held at December 31	0	0
Purchases and sales, net	(1)	(2)
Transfers into Level 3	0	0
Fair value of plan assets December 31	1	2
International \| Significant Unobservable Inputs (Level 3) \| Other
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets January 1	1	1
Actual return on plan assets:
Relating to assets still held at December 31	0	0
Purchases and sales, net	0	0
Transfers into Level 3	0	0
Fair value of plan assets December 31	$ 1	$ 1

No definition available.

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- Definition

Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets sold.

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- Definition

Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets still held.

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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- Definition

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.

+ References

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- Definition

Amount, measured using unobservable input, of increase (decrease) in plan asset of defined benefit plan from purchase, sale and settlement of trade associated with underlying investment.

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- Definition

Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan, for assets transferred into (out of) Level 3 of fair value hierarchy. Includes, but is not limited to, transfer due to change in observability of significant inputs.

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