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Pension and Other Postretirement Benefits - Narrative (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2020 | Jun. 30, 2020 | Sep. 30, 2019 | Mar. 31, 2019 | Sep. 30, 2020 | Sep. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Settlement charges | $ 3 |  | $ 4 |  | $ 67 | $ (8)
Restructuring and other charges | 22 |  | 56 |  | 166 | 572
Pension benefits |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Settlement charges | 8 |  | 4 |  | 72 | 8
Pension benefits | UK |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Settlement charges |  | $ 62 |  |  | 62 |
Pension benefits | Canada, UK, and US |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Settlement charges | 8 |  |  |  | 10 |
Pension benefits | US |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Settlement charges |  |  | 4 |  |  | 8
Other postretirement benefits |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Curtailment benefit | $ 2 |  | $ 0 |  | 2 | $ 58
Other postretirement benefits | US |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Curtailment benefit |  |  |  | $ 58 |  |
Decrease in obligation, pension benefits |  | $ (6) |  | 75 | $ (6) |
Other postretirement benefits | US | Accumulated other comprehensive loss |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Curtailment benefit |  |  |  | 17 |  |
Other postretirement benefits | US | Restructuring and other charges |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Curtailment benefit |  |  |  | 16 |  |
Other postretirement benefits | US | Discontinued operations |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Curtailment benefit |  |  |  | $ 42 |  |

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