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RETIREMENT PLANS - Rate Assumptions (Details) | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Pension Plans |  |  |
Weighted-average rates assumed in the actuarial calculations for the pension plan |  |  |
Discount rate for benefit obligation (as percent) | 2.60% | 4.20% | 4.70%
Discount rate for benefit cost (as percent) | 3.50% | 4.50% | 4.30%
Annual salary increase (as a percent) |  | 6.50% | 6.50%
Expected long-term return on plan assets (as a percent) | 5.10% | 6.10% | 6.10%
Postretirement Benefits |  |  |
Weighted-average rates assumed in the actuarial calculations for the pension plan |  |  |
Discount rate for benefit obligation (as percent) | 2.50% | 3.50% | 4.50%
Discount rate for benefit cost (as percent) | 3.50% | 4.50% | 3.90%
Postretirement Benefits | Medical benefit plan |  |  |
Health care cost trend rates |  |  |
Trend rate | 6.00% |  |
Ultimate rate | 4.00% |  |
Postretirement Benefits | Dental benefit plan |  |  |
Health care cost trend rates |  |  |
Ultimate rate | 4.00% |  |

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- Definition Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(1) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- Definition Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(1) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- Definition Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(3) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2919-114920 + Details
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- Definition Assumed rate, for next fiscal year, based on annual change in cost of health care cost benefits used to measure expected cost of benefits covered by defined benefit postretirement plan. Factors include, but are not limited to, estimate of health care inflation, change in health care utilization or delivery pattern, technological advances, and change in health status of participant. Excludes factors for change in composition of plan population by age and dependency status. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (l) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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