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Pension and Other Postretirement Benefit Plans - Fair Values of Pension Plan Assets (Details) - Pension Benefits - USD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | --- | ---
Significant Unobservable Inputs (Level 3) |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | $ 826 | $ 488 |
United States |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 9,648 | 10,896 | $ 9,766
United States | Fair Value, Inputs, Level 1, 2 and 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 5,532 | 5,189 |
United States | Fair Value, Inputs, Level 1, 2 and 3 | Cash and cash equivalents |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 40 | 6 |
United States | Fair Value, Inputs, Level 1, 2 and 3 | Developed markets equities, Investment funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 169 | 390 |
United States | Fair Value, Inputs, Level 1, 2 and 3 | Emerging markets equities, Investment funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 121 | 138 |
United States | Fair Value, Inputs, Level 1, 2 and 3 | Developed markets, Equity securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 2,172 | 2,743 |
United States | Fair Value, Inputs, Level 1, 2 and 3 | Government and agency obligations, Fixed income securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 1,509 | 757 |
United States | Fair Value, Inputs, Level 1, 2 and 3 | Corporate obligations, Fixed income securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 1,246 | 900 |
United States | Fair Value, Inputs, Level 1, 2 and 3 | Mortgage and asset backed-securities, Fixed income securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 262 | 240 |
United States | Fair Value, Inputs, Level 1, 2 and 3 | Other, Other investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 13 | 15 |
United States | Quoted Prices In Active Markets for Identical Assets (Level 1) |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 2,502 | 3,277 |
United States | Quoted Prices In Active Markets for Identical Assets (Level 1) | Cash and cash equivalents |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 40 | 6 |
United States | Quoted Prices In Active Markets for Identical Assets (Level 1) | Developed markets equities, Investment funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 169 | 390 |
United States | Quoted Prices In Active Markets for Identical Assets (Level 1) | Emerging markets equities, Investment funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 121 | 138 |
United States | Quoted Prices In Active Markets for Identical Assets (Level 1) | Developed markets, Equity securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 2,172 | 2,743 |
United States | Quoted Prices In Active Markets for Identical Assets (Level 1) | Government and agency obligations, Fixed income securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
United States | Quoted Prices In Active Markets for Identical Assets (Level 1) | Corporate obligations, Fixed income securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
United States | Quoted Prices In Active Markets for Identical Assets (Level 1) | Mortgage and asset backed-securities, Fixed income securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
United States | Quoted Prices In Active Markets for Identical Assets (Level 1) | Other, Other investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
United States | Significant Other Observable Inputs (Level 2) |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 3,017 | 1,897 |
United States | Significant Other Observable Inputs (Level 2) | Cash and cash equivalents |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
United States | Significant Other Observable Inputs (Level 2) | Developed markets equities, Investment funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
United States | Significant Other Observable Inputs (Level 2) | Emerging markets equities, Investment funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
United States | Significant Other Observable Inputs (Level 2) | Developed markets, Equity securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
United States | Significant Other Observable Inputs (Level 2) | Government and agency obligations, Fixed income securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 1,509 | 757 |
United States | Significant Other Observable Inputs (Level 2) | Corporate obligations, Fixed income securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 1,246 | 900 |
United States | Significant Other Observable Inputs (Level 2) | Mortgage and asset backed-securities, Fixed income securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 262 | 240 |
United States | Significant Other Observable Inputs (Level 2) | Other, Other investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
United States | Significant Unobservable Inputs (Level 3) |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 13 | 15 | 18
United States | Significant Unobservable Inputs (Level 3) | Cash and cash equivalents |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
United States | Significant Unobservable Inputs (Level 3) | Developed markets equities, Investment funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
United States | Significant Unobservable Inputs (Level 3) | Emerging markets equities, Investment funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
United States | Significant Unobservable Inputs (Level 3) | Real estate, Investment funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 | 0
United States | Significant Unobservable Inputs (Level 3) | Developed markets, Equity securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
United States | Significant Unobservable Inputs (Level 3) | Government and agency obligations, Fixed income securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
United States | Significant Unobservable Inputs (Level 3) | Corporate obligations, Fixed income securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
United States | Significant Unobservable Inputs (Level 3) | Mortgage and asset backed-securities, Fixed income securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
United States | Significant Unobservable Inputs (Level 3) | Insurance contracts, Other investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 | 0
United States | Significant Unobservable Inputs (Level 3) | Other, Other investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 13 | 15 | 18
United States | NAV |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 4,116 | 5,707 |
International |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 8,580 | 9,339 | 7,794
International | Fair Value, Inputs, Level 1, 2 and 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 8,119 | 8,537 |
International | Fair Value, Inputs, Level 1, 2 and 3 | Cash and cash equivalents |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 53 | 73 |
International | Fair Value, Inputs, Level 1, 2 and 3 | Developed markets equities, Investment funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 3,532 | 3,888 |
International | Fair Value, Inputs, Level 1, 2 and 3 | Emerging markets equities, Investment funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 168 | 238 |
International | Fair Value, Inputs, Level 1, 2 and 3 | Government and agency obligations, Investment funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 2,454 | 2,344 |
International | Fair Value, Inputs, Level 1, 2 and 3 | Corporate obligations, Investment funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 11 | 334 |
International | Fair Value, Inputs, Level 1, 2 and 3 | Fixed income obligations, Investment funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 11 | 11 |
International | Fair Value, Inputs, Level 1, 2 and 3 | Real estate, Investment funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 2 | 3 |
International | Fair Value, Inputs, Level 1, 2 and 3 | Developed markets, Equity securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 544 | 660 |
International | Fair Value, Inputs, Level 1, 2 and 3 | Government and agency obligations, Fixed income securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 293 | 268 |
International | Fair Value, Inputs, Level 1, 2 and 3 | Corporate obligations, Fixed income securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 114 | 119 |
International | Fair Value, Inputs, Level 1, 2 and 3 | Mortgage and asset backed-securities, Fixed income securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 55 | 55 |
International | Fair Value, Inputs, Level 1, 2 and 3 | Insurance contracts, Other investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 877 | 537 |
International | Fair Value, Inputs, Level 1, 2 and 3 | Other, Other investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 5 | 7 |
International | Quoted Prices In Active Markets for Identical Assets (Level 1) |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 1,497 | 1,602 |
International | Quoted Prices In Active Markets for Identical Assets (Level 1) | Cash and cash equivalents |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 50 | 54 |
International | Quoted Prices In Active Markets for Identical Assets (Level 1) | Developed markets equities, Investment funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 461 | 562 |
International | Quoted Prices In Active Markets for Identical Assets (Level 1) | Emerging markets equities, Investment funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 56 | 62 |
International | Quoted Prices In Active Markets for Identical Assets (Level 1) | Government and agency obligations, Investment funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 372 | 249 |
International | Quoted Prices In Active Markets for Identical Assets (Level 1) | Corporate obligations, Investment funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 4 | 5 |
International | Quoted Prices In Active Markets for Identical Assets (Level 1) | Fixed income obligations, Investment funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 7 | 7 |
International | Quoted Prices In Active Markets for Identical Assets (Level 1) | Real estate, Investment funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
International | Quoted Prices In Active Markets for Identical Assets (Level 1) | Developed markets, Equity securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 544 | 660 |
International | Quoted Prices In Active Markets for Identical Assets (Level 1) | Government and agency obligations, Fixed income securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 2 | 2 |
International | Quoted Prices In Active Markets for Identical Assets (Level 1) | Corporate obligations, Fixed income securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 1 | 1 |
International | Quoted Prices In Active Markets for Identical Assets (Level 1) | Mortgage and asset backed-securities, Fixed income securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
International | Quoted Prices In Active Markets for Identical Assets (Level 1) | Insurance contracts, Other investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
International | Quoted Prices In Active Markets for Identical Assets (Level 1) | Other, Other investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
International | Significant Other Observable Inputs (Level 2) |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 5,809 | 6,462 |
International | Significant Other Observable Inputs (Level 2) | Cash and cash equivalents |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 3 | 19 |
International | Significant Other Observable Inputs (Level 2) | Developed markets equities, Investment funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 3,071 | 3,326 |
International | Significant Other Observable Inputs (Level 2) | Emerging markets equities, Investment funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 112 | 176 |
International | Significant Other Observable Inputs (Level 2) | Government and agency obligations, Investment funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 2,082 | 2,095 |
International | Significant Other Observable Inputs (Level 2) | Corporate obligations, Investment funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 7 | 329 |
International | Significant Other Observable Inputs (Level 2) | Fixed income obligations, Investment funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 4 | 4 |
International | Significant Other Observable Inputs (Level 2) | Real estate, Investment funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 1 | 1 |
International | Significant Other Observable Inputs (Level 2) | Developed markets, Equity securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
International | Significant Other Observable Inputs (Level 2) | Government and agency obligations, Fixed income securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 291 | 266 |
International | Significant Other Observable Inputs (Level 2) | Corporate obligations, Fixed income securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 113 | 118 |
International | Significant Other Observable Inputs (Level 2) | Mortgage and asset backed-securities, Fixed income securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 55 | 55 |
International | Significant Other Observable Inputs (Level 2) | Insurance contracts, Other investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 66 | 67 |
International | Significant Other Observable Inputs (Level 2) | Other, Other investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 4 | 6 |
International | Significant Unobservable Inputs (Level 3) |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 813 | 473 | 417
International | Significant Unobservable Inputs (Level 3) | Cash and cash equivalents |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
International | Significant Unobservable Inputs (Level 3) | Developed markets equities, Investment funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
International | Significant Unobservable Inputs (Level 3) | Emerging markets equities, Investment funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
International | Significant Unobservable Inputs (Level 3) | Government and agency obligations, Investment funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
International | Significant Unobservable Inputs (Level 3) | Corporate obligations, Investment funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
International | Significant Unobservable Inputs (Level 3) | Fixed income obligations, Investment funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
International | Significant Unobservable Inputs (Level 3) | Real estate, Investment funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 1 | 2 | 4
International | Significant Unobservable Inputs (Level 3) | Developed markets, Equity securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
International | Significant Unobservable Inputs (Level 3) | Government and agency obligations, Fixed income securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
International | Significant Unobservable Inputs (Level 3) | Corporate obligations, Fixed income securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
International | Significant Unobservable Inputs (Level 3) | Mortgage and asset backed-securities, Fixed income securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 0 | 0 |
International | Significant Unobservable Inputs (Level 3) | Insurance contracts, Other investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 811 | 470 | 412
International | Significant Unobservable Inputs (Level 3) | Other, Other investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 1 | 1 | $ 1
International | NAV |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | $ 461 | $ 802 |

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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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