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Pension and Other Postretirement Benefits - Additional Information (Details) $ in Millions |  |  | 1 Months Ended | 3 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | --- | ---
Jul. 25, 2019 employee | Apr. 13, 2018 employee | Jun. 30, 2019 employee | Dec. 31, 2018 USD ($) | Jun. 30, 2018 USD ($) | Jun. 30, 2018 USD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($)
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |  |
Offset to AOCI, net of tax |  |  |  |  |  |  | $ (388) | $ 255 | $ (220)
Curtailment (charge) benefit |  |  |  |  |  | $ (9) |  |  |
Number of employees included in Labor Agreement | employee | 560 | 1,300 | 3,400 |  |  |  |  |  |
Employees subject to retirement benefit increase under Labor Agreement | employee |  | 300 |  |  |  |  |  |  |
Labor agreement, number of years covered | 4 years |  | 3 years |  |  |  |  |  |
Labor agreement, one time signing bonus |  |  |  |  |  |  | 9 |  |
Duration of labor agreement |  | 5 years |  |  |  |  |  |  |
Restructuring and other charges |  |  |  |  |  |  | 620 | 9 | 165
Pension benefits |  |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |  |
Curtailment (charge) benefit |  |  |  |  |  |  | 0 | (23) | 0
Other postretirement benefits |  |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |  |
Decrease in pension liability, plan amendment |  |  |  |  |  |  |  | 32 |
Offset to AOCI, net of tax |  |  |  | $ 13 |  |  |  | 4 |
Curtailment (charge) benefit |  |  |  | $ (9) |  |  | 58 | 28 | $ 0
United States | Pension benefits |  |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |  |
Decrease in pension liability, plan amendment |  |  |  |  | $ 136 |  | 75 |  |
Offset to AOCI, net of tax |  |  |  |  | 141 |  |  |  |
Curtailment (charge) benefit |  |  |  |  | $ (5) |  | (17) |  |
Pension Settlement Cost |  |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |  |
Restructuring and other charges |  |  |  |  |  |  | $ 9 | $ 96 |

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