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Pension and Other Postretirement Benefits - Summary of Information in Curtailment or Settlement of Benefits Requiring Remeasurement, Update to Discount Rates Used to Determine Benefit Obligations of Affected Plans (Detail) $ in Millions | 6 Months Ended |  |
--- | --- | --- | ---
Jun. 30, 2021 USD ($) Employee | Mar. 31, 2021 | Dec. 31, 2020
Action# 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Number of affected plan participants | Employee | 840 |  |
Weighted average discount rate |  | 3.06% | 2.45%
Plan remeasurement date | Mar. 31, 2021 |  |
Decrease to accrued other postretirement benefits liability | $ (106) |  |
Curtailments | (17) |  |
Settlements | $ 26 |  |
Action# 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Number of affected plan participants | Employee | 120 |  |
Weighted average discount rate | 2.71% |  | 2.38%
Plan remeasurement date | Jun. 30, 2021 |  |
Decrease to accrued pension benefits liability | $ (90) |  |
Settlements | $ 39 |  |

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