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Pension and Other Postretirement Benefits - Schedule of Fair Value of Pension Plan Assets (Detail) - USD ($) $ in Millions | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
--- | --- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net receivables which represents assets related to divested businesses to be transferred to the buyers | $ 28 | $ 20 |
Pension benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 4,862 | 4,666 | $ 10,928
Fair Value, Measurements, Recurring | Pension benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 4,834 | 4,646 |
Defined benefit plan, alternative investments, fair value of plan asset | 2,932 | 2,878 |
Fair Value, Measurements, Recurring | Pension benefits | Equities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 1,357 | 1,395 |
Defined benefit plan, alternative investments, fair value of plan asset | 978 | 1,002 |
Fair Value, Measurements, Recurring | Pension benefits | Equities | Equity Funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 972 | 824 |
Defined benefit plan, alternative investments, fair value of plan asset | 593 | 431 |
Fair Value, Measurements, Recurring | Pension benefits | Equities | Hedge Funds, Equity |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 230 | 406 |
Defined benefit plan, alternative investments, fair value of plan asset | 230 | 406 |
Fair Value, Measurements, Recurring | Pension benefits | Equities | Private Equity Funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 155 | 165 |
Defined benefit plan, alternative investments, fair value of plan asset | 155 | 165 |
Fair Value, Measurements, Recurring | Pension benefits | Fixed income |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 2,278 | 1,958 |
Defined benefit plan, alternative investments, fair value of plan asset | 924 | 729 |
Fair Value, Measurements, Recurring | Pension benefits | Fixed income | Intermediate and Long Duration Government Credit |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 1,961 | 773 |
Defined benefit plan, alternative investments, fair value of plan asset | 779 | 655 |
Fair Value, Measurements, Recurring | Pension benefits | Fixed income | Other Funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 317 | 1,185 |
Defined benefit plan, alternative investments, fair value of plan asset | 145 | 74 |
Fair Value, Measurements, Recurring | Pension benefits | Other investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 1,199 | 1,293 |
Defined benefit plan, alternative investments, fair value of plan asset | 1,030 | 1,147 |
Fair Value, Measurements, Recurring | Pension benefits | Other investments | Other Funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 359 | 243 |
Defined benefit plan, alternative investments, fair value of plan asset | 275 | 178 |
Fair Value, Measurements, Recurring | Pension benefits | Other investments | Real Estate Funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 257 | 266 |
Defined benefit plan, alternative investments, fair value of plan asset | 172 | 185 |
Fair Value, Measurements, Recurring | Pension benefits | Other investments | Discretionary And Systematic Macro Hedge Funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 583 | 784 |
Defined benefit plan, alternative investments, fair value of plan asset | 583 | 784 |
Fair Value, Measurements, Recurring | Pension benefits | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 906 | 1,622 |
Fair Value, Measurements, Recurring | Pension benefits | Level 1 | Equities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 379 | 393 |
Fair Value, Measurements, Recurring | Pension benefits | Level 1 | Equities | Equity Funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 379 | 393 |
Fair Value, Measurements, Recurring | Pension benefits | Level 1 | Equities | Hedge Funds, Equity |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension benefits | Level 1 | Equities | Private Equity Funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension benefits | Level 1 | Fixed income |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 365 | 1,083 |
Fair Value, Measurements, Recurring | Pension benefits | 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 | 201 | 23 |
Fair Value, Measurements, Recurring | Pension benefits | Level 1 | Fixed income | Other Funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 164 | 1,060 |
Fair Value, Measurements, Recurring | Pension benefits | Level 1 | Other investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 162 | 146 |
Fair Value, Measurements, Recurring | Pension benefits | Level 1 | Other investments | Other Funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 77 | 65 |
Fair Value, Measurements, Recurring | Pension benefits | Level 1 | Other investments | Real Estate Funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 85 | 81 |
Fair Value, Measurements, Recurring | Pension benefits | 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 |
Fair Value, Measurements, Recurring | Pension benefits | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 996 | 146 |
Fair Value, Measurements, Recurring | Pension benefits | Level 2 | Equities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension benefits | Level 2 | Equities | Equity Funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension benefits | Level 2 | Equities | Hedge Funds, Equity |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension benefits | Level 2 | Equities | Private Equity Funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension benefits | Level 2 | Fixed income |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 989 | 146 |
Fair Value, Measurements, Recurring | Pension benefits | 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 | 981 | 95 |
Fair Value, Measurements, Recurring | Pension benefits | Level 2 | Fixed income | Other Funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 8 | 51 |
Fair Value, Measurements, Recurring | Pension benefits | Level 2 | Other investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 7 | 0 |
Fair Value, Measurements, Recurring | Pension benefits | Level 2 | Other investments | Other Funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 7 | 0 |
Fair Value, Measurements, Recurring | Pension benefits | Level 2 | Other investments | Real Estate Funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of pension and other postretirement plans' assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension benefits | 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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