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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

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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. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(02)(A) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=112275985&loc=d3e4179-114921 + Details
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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 Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 4: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=112275985&loc=d3e4179-114921 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 6: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 + Details
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