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Pension and Other Postretirement Benefits - Schedule of Fair Value of Pension Plan Assets (Details) - USD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net receivables which represents assets related to divested businesses to be transferred to the buyers | $ 1 | $ 28 |
Pension benefits paid |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 4,334 | 4,862 | $ 4,666
Defined benefit plan, alternative investments, fair value of plan asset | 2,726 | 2,932 |
Net plan assets, excluding net receivables from securities purchased and sold but not yet settled plus interest and dividends earned on various investments | 4,333 |  |
Net plan assets excluding certain net receivables |  | 4,834 |
Pension benefits paid | Equities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 1,275 | 1,357 |
Defined benefit plan, alternative investments, fair value of plan asset | 957 | 978 |
Pension benefits paid | Equities | Equity securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 896 | 972 |
Defined benefit plan, alternative investments, fair value of plan asset | 578 | 593 |
Pension benefits paid | Equities | Long/short equity hedge funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 232 | 230 |
Defined benefit plan, alternative investments, fair value of plan asset | 232 | 230 |
Pension benefits paid | Equities | Private equity |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 147 | 155 |
Defined benefit plan, alternative investments, fair value of plan asset | 147 | 155 |
Pension benefits paid | Fixed income |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 2,074 | 2,278 |
Defined benefit plan, alternative investments, fair value of plan asset | 922 | 924 |
Pension benefits paid | Fixed income | Intermediate and long duration government/credit |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 1,904 | 1,961 |
Defined benefit plan, alternative investments, fair value of plan asset | 770 | 779 |
Pension benefits paid | Fixed income | Other |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 170 | 317 |
Defined benefit plan, alternative investments, fair value of plan asset | 152 | 145 |
Pension benefits paid | Other investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 984 | 1,199 |
Defined benefit plan, alternative investments, fair value of plan asset | 847 | 1,030 |
Pension benefits paid | Other investments | Other |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 268 | 359 |
Defined benefit plan, alternative investments, fair value of plan asset | 212 | 275 |
Pension benefits paid | Other investments | Real estate |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 245 | 257 |
Defined benefit plan, alternative investments, fair value of plan asset | 164 | 172 |
Pension benefits paid | Other investments | Discretionary and systematic macro hedge funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 471 | 583 |
Defined benefit plan, alternative investments, fair value of plan asset | 471 | 583 |
Pension benefits paid | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 664 | 906 |
Pension benefits paid | Level 1 | Equities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 318 | 379 |
Pension benefits paid | Level 1 | Equities | Equity securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 318 | 379 |
Pension benefits paid | Level 1 | Equities | Long/short equity hedge funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 0 | 0 |
Pension benefits paid | Level 1 | Equities | Private equity |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 0 | 0 |
Pension benefits paid | Level 1 | Fixed income |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 209 | 365 |
Pension benefits paid | Level 1 | Fixed income | Intermediate and long duration government/credit |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 200 | 201 |
Pension benefits paid | Level 1 | Fixed income | Other |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 9 | 164 |
Pension benefits paid | Level 1 | Other investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 137 | 162 |
Pension benefits paid | Level 1 | Other investments | Other |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 56 | 77 |
Pension benefits paid | Level 1 | Other investments | Real estate |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 81 | 85 |
Pension benefits paid | Level 1 | Other investments | Discretionary and systematic macro hedge funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 0 | 0 |
Pension benefits paid | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 943 | 996 |
Pension benefits paid | Level 2 | Equities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 0 | 0 |
Pension benefits paid | Level 2 | Equities | Equity securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 0 | 0 |
Pension benefits paid | Level 2 | Equities | Long/short equity hedge funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 0 | 0 |
Pension benefits paid | Level 2 | Equities | Private equity |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 0 | 0 |
Pension benefits paid | Level 2 | Fixed income |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 943 | 989 |
Pension benefits paid | Level 2 | Fixed income | Intermediate and long duration government/credit |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 934 | 981 |
Pension benefits paid | Level 2 | Fixed income | Other |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 9 | 8 |
Pension benefits paid | Level 2 | Other investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 0 | 7 |
Pension benefits paid | Level 2 | Other investments | Other |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 0 | 7 |
Pension benefits paid | Level 2 | Other investments | Real estate |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 0 | 0 |
Pension benefits paid | Level 2 | Other investments | Discretionary and systematic macro hedge funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | $ 0 | $ 0 |

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