RETIREMENT AND POSTRETIREMENT BENEFIT PLANS - ASSUMPTIONS (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Pension Benefits
Benefit Obligation Assumptions:
Discount rate	2.19%	3.09%
Rate of increase in compensation levels	5.07%	5.32%
Net Periodic Benefit Cost Assumptions:
Discount rate	3.04%	3.22%
Rate of increase in compensation levels	5.34%	5.35%
Assumed long-term rate of return on assets	6.02%	6.03%
Net decrease in pension plan obligations	$ 8
Postretirement Benefits
Benefit Obligation Assumptions:
Discount rate	3.05%	3.26%
Rate of increase in compensation levels	0.00%	0.00%
Net Periodic Benefit Cost Assumptions:
Discount rate	3.26%	3.41%
Rate of increase in compensation levels	0.00%	0.00%
Assumed long-term rate of return on assets	0.00%	0.00%
Net decrease in postretirement plan obligations	$ 12
Postretirement Benefits \| MAPD
Assumed healthcare cost trend rates
Projected annual rates of healthcare cost trend rates, year nine and beyond (as a percent)	4.50%
Postretirement Benefits \| MAPD \| Low end of range
Assumed healthcare cost trend rates
Projected annual rates of healthcare cost trend rates, next fiscal year (as a percent)	9.60%
Postretirement Benefits \| Non-MAPD
Assumed healthcare cost trend rates
Projected annual rates of healthcare cost trend rates, year nine and beyond (as a percent)	4.50%
Postretirement Benefits \| Non-MAPD \| Low end of range
Assumed healthcare cost trend rates
Health care cost trend rates for current year (as a percent)	6.50%
Postretirement Benefits \| Non-MAPD \| High end of range
Assumed healthcare cost trend rates
Health care cost trend rates for current year (as a percent)	7.00%

Defined Benefit Plan, Health Care Cost Trend Rate Assumed

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Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Year Nine And Thereafter

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Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan.

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Weighted average rate increase of compensation, used to determine benefit obligation of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan.

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Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost of defined benefit plan.

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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
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-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

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-Publisher FASB
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Weighted average rate of compensation increase used to determine net periodic benefit cost of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan.

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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.

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Amount of increase (decrease) in obligation for pension benefits. Includes, but is not limited to, defined benefit or defined contribution plans. Excludes other postretirement benefits.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

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Amount of increase (decrease) in obligation for other postretirement benefits. Includes, but is not limited to, defined benefit and defined contribution plans. Excludes pension benefits.

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