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Pension and Other Postretirement Benefits - Narrative (Details) - USD ($) $ in Millions |  | 1 Months Ended | 3 Months Ended
--- | --- | --- | ---
Nov. 01, 2016 | Apr. 30, 2019 | Mar. 31, 2018 | Apr. 30, 2017 | Mar. 31, 2019 | Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Restructuring and other charges (benefits) |  |  |  |  | $ 12 | $ 7
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits |  |  |  |  | 40 | 143
Aggregate cash cash contribution to pension plan | $ 150 |  |  |  |  |
Cash contribution term to pension plan | 30 months |  |  |  |  |
Cash payments made for pension and other post-retirement benefits |  |  | $ 66 | $ 50 |  |
Other postretirement benefits |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Curtailment benefit (charges) |  |  |  |  | 58 | 0
Pension Plan |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Curtailment benefit (charges) |  |  |  |  | 0 | (5)
UNITED STATES | Other postretirement benefits |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Decrease in obligation, pension benefits |  |  |  |  | (63) |
Curtailment benefit (charges) |  |  |  |  | (58) |
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits |  |  |  |  | (5) |
UNITED STATES | Pension Plan |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Decrease in obligation, pension benefits |  |  |  |  |  | (136)
Curtailment benefit (charges) |  |  |  |  |  | 5
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits |  |  |  |  |  | $ 141
Subsequent Event |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Cash payments made for pension and other post-retirement benefits |  | $ 34 |  |  |  |
Pension Settlement Cost |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Restructuring and other charges (benefits) |  |  |  |  | 2 |
Elimination Of Health Care Subsidies | UNITED STATES | Other postretirement benefits |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Decrease in obligation, pension benefits |  |  |  |  | $ (12) |

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