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PENSIONS AND OTHER POSTRETIREMENT BENEFITS - Multiemployer Plan (Details) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($)
Multiemployer Plan [Line Items] |  |  |
Contributions | $ 30 | $ 4 | $ 4
Steelworkers Pension Trust |  |  |
Multiemployer Plan [Line Items] |  |  |
Pension Plan EIN | 236648508 |  |
Pension Plan Number | 499 |  |
Pension Protection Act Zone Status | Green | Green |
FIP/RP Status Pending/Implemented | No |  |
Contributions | $ 14 | $ 4 | $ 4
Surcharge Imposed | No |  |
Multiemployer Plan, Pension, Significant, Accumulated Benefit Obligation |  | 5,748 |
Multiemployer Plan, Pension, Significant, Plan Asset |  | $ 5,372 |
Multiemployer Plan, Pension, Significant, Funded Status Percentage |  | 0.93 |
Steelworkers Pension Trust | ArcelorMittal USA and AK Steel [Member] |  |  |
Multiemployer Plan [Line Items] |  |  |
Multiemployer Plan, Pension, Significant, Contribution, Percentage |  | 0.30 | 0.30
Steelworkers Pension Trust | Other Companies |  |  |
Multiemployer Plan [Line Items] |  |  |
Multiemployer Plan, Pension, Significant, Contribution, Percentage |  | 0.05 | 0.05
Steelworkers Pension Trust | Minimum [Member] |  |  |
Multiemployer Plan [Line Items] |  |  |
Expiration Date of Collective Bargaining Agreement | Jan. 22, 2021 |  |
Steelworkers Pension Trust | Maximum [Member] |  |  |
Multiemployer Plan [Line Items] |  |  |
Expiration Date of Collective Bargaining Agreement | Oct. 01, 2022 |  |
IAM National Pension Fund's National Pension Plan |  |  |
Multiemployer Plan [Line Items] |  |  |
Pension Plan EIN | 516031295 |  |
Pension Plan Number | 002 |  |
Pension Protection Act Zone Status | Red | Green |
FIP/RP Status Pending/Implemented | Implemented |  |
Contributions | $ 16 | $ 0 | $ 0
Surcharge Imposed | Yes |  |
IAM National Pension Fund's National Pension Plan | Minimum [Member] |  |  |
Multiemployer Plan [Line Items] |  |  |
Expiration Date of Collective Bargaining Agreement | May 31, 2022 |  |
IAM National Pension Fund's National Pension Plan | Maximum [Member] |  |  |
Multiemployer Plan [Line Items] |  |  |
Expiration Date of Collective Bargaining Agreement | May 15, 2023 |  |
American Maritime Officers Plan |  |  |
Multiemployer Plan [Line Items] |  |  |
Pension Plan EIN | 131936709 |  |
Pension Plan Number | 001 |  |
Pension Protection Act Zone Status | Green | Green |
FIP/RP Status Pending/Implemented | No |  |
Contributions | $ 0 | $ 0 | $ 0
Surcharge Imposed | No |  |
Expiration Date of Collective Bargaining Agreement | Jul. 31, 2021 |  |

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- Definition Amount of cost for employer contribution to multiemployer plan. Multiemployer plan includes, but is not limited to, pension plan determined to be individually significant and insignificant and other postretirement benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=35742348&loc=SL14450788-114948 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 35 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=29639808&loc=d3e29008-114946 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450702-114947 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 9 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450691-114947 + Details
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