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Pension and Other Postretirement Benefits - Narrative (Details) $ in Millions |  |  |  | 1 Months Ended | 3 Months Ended | 9 Months Ended
--- | --- | --- | --- | --- | --- | ---
Jul. 25, 2019 employee | Apr. 13, 2018 employee | Nov. 01, 2016 USD ($) | Jun. 30, 2019 location employee | Apr. 30, 2019 USD ($) | Mar. 31, 2018 USD ($) | Apr. 30, 2017 USD ($) | Sep. 30, 2019 USD ($) | Jun. 30, 2019 USD ($) | Mar. 31, 2019 USD ($) | Sep. 30, 2018 USD ($) | Jun. 30, 2018 USD ($) | Mar. 31, 2018 USD ($) | Sep. 30, 2019 USD ($) | Sep. 30, 2018 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Curtailment benefit (charges) |  |  |  |  |  |  |  |  |  |  |  | $ (9) |  |  |
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits |  |  |  |  |  |  |  | $ 26 |  |  | $ 37 |  |  | $ 89 | $ 209
Aggregate cash contribution to pension plan |  |  | $ 150 |  |  |  |  |  |  |  |  |  |  |  |
Cash contribution term to pension plan |  |  | 30 months |  |  |  |  |  |  |  |  |  |  |  |
Cash payments made for pension and other post-retirement benefits |  |  |  |  | $ 34 | $ 66 | $ 50 |  |  |  |  |  |  |  |
Restructuring and other charges (benefits) |  |  |  |  |  |  |  | 119 |  |  | (2) |  |  | 630 | 20
Labor agreement term | 4 years | 5 years |  | 3 years |  |  |  |  |  |  |  |  |  |  |
Number of employees included in Labor Agreement | employee | 560 | 1,300 |  | 3,400 |  |  |  |  |  |  |  |  |  |  |
Labor agreement, number of locations covered | location |  |  |  | 4 |  |  |  |  |  |  |  |  |  |  |
Labor agreement, one time signing bonus |  |  |  |  |  |  |  |  | $ 9 |  |  |  |  |  |
Employees subject to retirement benefit increase under Labor Agreement | employee |  | 300 |  |  |  |  |  |  |  |  |  |  |  |  |
Other postretirement benefits |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Decrease in obligation, pension benefits |  |  |  |  |  |  |  |  |  | $ 63 | 32 |  |  |  |
Curtailment benefit (charges) |  |  |  |  |  |  |  | 0 |  | (58) | 28 |  |  | 58 | 28
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits |  |  |  |  |  |  |  |  |  | 5 | 4 |  |  |  |
Pension Plan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Decrease in obligation, pension benefits |  |  |  |  |  |  |  |  |  |  |  |  | $ 136 |  |
Curtailment benefit (charges) |  |  |  |  |  |  |  | 0 |  |  | 0 |  | 5 | 0 | (14)
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits |  |  |  |  |  |  |  |  |  |  |  |  | $ 141 |  |
Pension Settlement Cost |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Restructuring and other charges (benefits) |  |  |  |  |  |  |  | $ 4 |  |  | $ 4 |  |  | $ 8 | $ 4
Elimination Of Health Care Subsidies | Other postretirement benefits |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Decrease in obligation, pension benefits |  |  |  |  |  |  |  |  |  | $ 12 |  |  |  |  |

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