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Employee Benefits - Schedule of Fair Value of U.S Plan Assets (Details) - Pension Plan - USD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | --- | ---
U.S. |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | $ 1,796 | $ 1,958 | $ 1,683
U.S. | Cash and cash equivalents |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 130 | 56 |
U.S. | Large cap domestic |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 294 | 313 |
U.S. | Small cap domestic |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 14 | 17 |
U.S. | International |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 76 | 90 |
U.S. | Equity derivatives |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | (14) | 111 |
U.S. | International pooled funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 235 | 270 |
U.S. | Pooled funds large cap domestic |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 8 | 12 |
U.S. | Pooled funds small cap domestic |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 42 | 114 |
U.S. | Corporate bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 111 | 110 |
U.S. | Government and agency bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 126 | 148 |
U.S. | Asset-backed securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 2 |  |
U.S. | Government and agency bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 95 |  |
U.S. | Corporate Bonds And Pooled Funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 322 | 290 |
U.S. | Real estate and REITS |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 78 | 82 |
U.S. | Alternative investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 277 | 345 |
U.S. | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 687 | 672 |
U.S. | Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash and cash equivalents |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 130 | 56 |
U.S. | Quoted Prices in Active Markets for Identical Assets (Level 1) | Large cap domestic |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 294 | 313 |
U.S. | Quoted Prices in Active Markets for Identical Assets (Level 1) | Small cap domestic |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 14 | 17 |
U.S. | Quoted Prices in Active Markets for Identical Assets (Level 1) | International |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 76 | 90 |
U.S. | Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity derivatives |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 | 0 |
U.S. | Quoted Prices in Active Markets for Identical Assets (Level 1) | International pooled funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 | 0 |
U.S. | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pooled funds large cap domestic |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 |  |
U.S. | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pooled funds small cap domestic |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 | 0 |
U.S. | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 | 0 |
U.S. | Quoted Prices in Active Markets for Identical Assets (Level 1) | Government and agency bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 95 | 114 |
U.S. | Quoted Prices in Active Markets for Identical Assets (Level 1) | Asset-backed securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 |  |
U.S. | Quoted Prices in Active Markets for Identical Assets (Level 1) | Government and agency bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 |  |
U.S. | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate Bonds And Pooled Funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 | 0 |
U.S. | Quoted Prices in Active Markets for Identical Assets (Level 1) | Real estate and REITS |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 78 | 82 |
U.S. | Quoted Prices in Active Markets for Identical Assets (Level 1) | Alternative investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 | 0 |
U.S. | Significant Other Observable Inputs (Level 2) |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 130 | 255 |
U.S. | Significant Other Observable Inputs (Level 2) | Cash and cash equivalents |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 | 0 |
U.S. | Significant Other Observable Inputs (Level 2) | Large cap domestic |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 | 0 |
U.S. | Significant Other Observable Inputs (Level 2) | Small cap domestic |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 | 0 |
U.S. | Significant Other Observable Inputs (Level 2) | International |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 | 0 |
U.S. | Significant Other Observable Inputs (Level 2) | Equity derivatives |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | (14) | 111 |
U.S. | Significant Other Observable Inputs (Level 2) | International pooled funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 | 0 |
U.S. | Significant Other Observable Inputs (Level 2) | Pooled funds large cap domestic |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 |  |
U.S. | Significant Other Observable Inputs (Level 2) | Pooled funds small cap domestic |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 | 0 |
U.S. | Significant Other Observable Inputs (Level 2) | Corporate bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 111 | 110 |
U.S. | Significant Other Observable Inputs (Level 2) | Government and agency bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 31 | 34 |
U.S. | Significant Other Observable Inputs (Level 2) | Asset-backed securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 2 |  |
U.S. | Significant Other Observable Inputs (Level 2) | Government and agency bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 |  |
U.S. | Significant Other Observable Inputs (Level 2) | Corporate Bonds And Pooled Funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 | 0 |
U.S. | Significant Other Observable Inputs (Level 2) | Real estate and REITS |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 | 0 |
U.S. | Significant Other Observable Inputs (Level 2) | Alternative investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 | 0 |
U.S. | Significant Unobservable Inputs (Level 3) |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 | 0 |
U.S. | Significant Unobservable Inputs (Level 3) | Cash and cash equivalents |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 | 0 |
U.S. | Significant Unobservable Inputs (Level 3) | Large cap domestic |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 | 0 |
U.S. | Significant Unobservable Inputs (Level 3) | Small cap domestic |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 | 0 |
U.S. | Significant Unobservable Inputs (Level 3) | International |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 | 0 |
U.S. | Significant Unobservable Inputs (Level 3) | Equity derivatives |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 | 0 |
U.S. | Significant Unobservable Inputs (Level 3) | International pooled funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 | 0 |
U.S. | Significant Unobservable Inputs (Level 3) | Pooled funds large cap domestic |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 |  |
U.S. | Significant Unobservable Inputs (Level 3) | Pooled funds small cap domestic |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 | 0 |
U.S. | Significant Unobservable Inputs (Level 3) | Corporate bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 | 0 |
U.S. | Significant Unobservable Inputs (Level 3) | Government and agency bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 | 0 |
U.S. | Significant Unobservable Inputs (Level 3) | Asset-backed securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 |  |
U.S. | Significant Unobservable Inputs (Level 3) | Government and agency bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 |  |
U.S. | Significant Unobservable Inputs (Level 3) | Corporate Bonds And Pooled Funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 | 0 |
U.S. | Significant Unobservable Inputs (Level 3) | Real estate and REITS |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 | 0 |
U.S. | Significant Unobservable Inputs (Level 3) | Alternative investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 | 0 |
U.K. |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 5,225 | 5,906 | $ 5,675
U.K. | Cash and cash equivalents |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 96 | 209 |
U.K. | Alternative investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 694 | 911 |
U.K. | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 2,175 | 2,571 |
U.K. | Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash and cash equivalents |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 96 | 209 |
U.K. | Quoted Prices in Active Markets for Identical Assets (Level 1) | Alternative investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 | 0 |
U.K. | Significant Other Observable Inputs (Level 2) |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | (582) | (346) |
U.K. | Significant Other Observable Inputs (Level 2) | Cash and cash equivalents |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 | 0 |
U.K. | Significant Other Observable Inputs (Level 2) | Alternative investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 | 0 |
U.K. | Significant Unobservable Inputs (Level 3) |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 1,688 | 1,909 |
U.K. | Significant Unobservable Inputs (Level 3) | Cash and cash equivalents |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | 0 | 0 |
U.K. | Significant Unobservable Inputs (Level 3) | Alternative investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total | $ 0 | $ 0 |

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