Retirement Plans (Schedule Of Pension Plan Asset Allocation) (Details)	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Target average rate of return	6.25%	7.00%
Asset allocation	100.00%	100.00%
Average long-term rate of return target description	The investment strategy for pension plan assets is to maintain a broadly diversified portfolio designed to achieve our target average long-term rate of return. We decreased the expected rate of return for 2021 from 7% to 6.25% due to a shift of certain assets from equity to debt in alignment with our 2021 target asset allocation.
Weighted-average maturity of Pension Plan debt portfolio	17 years	14 years
Prohibited investments description	The investment of pension plan assets in securities issued by UPC is explicitly prohibited by the plan for both the equity and debt portfolios, other than through index fund holdings.
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset allocation	63.00%	63.00%
Equity Securities [Member] \| Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target average rate of return	50.00%
Equity Securities [Member] \| Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target average rate of return	60.00%
Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset allocation	34.00%	31.00%
Debt Securities [Member] \| Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target average rate of return	40.00%
Debt Securities [Member] \| Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target average rate of return	50.00%
Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset allocation	3.00%	6.00%
Real Estate [Member] \| Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target average rate of return	0.00%
Real Estate [Member] \| Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target average rate of return	2.00%

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+ References

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Description of investment policy and strategy for defined benefit plan asset. Includes, but is not limited to, investment allocation decision and factor pertinent to understanding investment policy and strategy for plan asset. Factor includes, but is not limited to, investment goal, risk management practice, permitted and prohibited investment including use of derivative, diversification, and relationship between plan asset and obligation.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

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Description of basis used to determine overall expected long-term rate-of-return assumption for plan asset of defined benefit plan. Includes, but is not limited to, approach used, and extent approach was based on historical return and adjustment made to reflect expectation of future return.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(iii)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

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Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 55
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

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