Benefit Plans - Actuarial Assumptions and Year-End Asset Allocations (Details)	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Pension and Supplemental Executive Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Discount Rate Used to Determine Benefit Obligation(in hundredths)	2.75%	3.45%
Rate of Compensation Increase Used to Determine Benefit Obligation (in hundredths)	3.00%	3.00%
Cash Balance Interest Crediting Rate Used to Determine Benefit Obligation (in hundredths)	2.50%	3.20%
Discount Rate Used to Determine Net Periodic Benefit Cost (in hundredths)	3.30%	4.40%
Expected Long-term Return on Plan Assets Used to Determine Net Periodic Benefit Cost (in hundredths)	5.75%	5.75%
Rate of Compensation Increase Used to Determine Net Periodic Benefit Cost (in hundredths)	3.00%	3.00%
Other Postretirement Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Discount Rate Used to Determine Benefit Obligation(in hundredths)	2.35%	3.20%
Discount Rate Used to Determine Net Periodic Benefit Cost (in hundredths)	3.20%	4.25%
Expected Long-term Return on Plan Assets Used to Determine Net Periodic Benefit Cost (in hundredths)	7.50%	7.50%
Health Care Cost Trend Rate Assumed for Next Year (in hundredths)	6.00%	6.00%
Rate to Which the Cost Trend Rate is Assumed to Decline (Ultimate Trend Rate) (in hundredths)	5.00%	5.00%
Weighted-average asset allocations of plans (in hundredths)	100.00%	100.00%
Other Postretirement Benefit Plan \| Equity securities
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocations of plans (in hundredths)	100.00%	100.00%
Other Postretirement Benefit Plan \| Total fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocations of plans (in hundredths)	0.00%	0.00%
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocations of plans (in hundredths)	100.00%	100.00%
Pension Plan \| Equity securities
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocations of plans (in hundredths)	21.00%	23.00%
Pension Plan \| Total fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocations of plans (in hundredths)	79.00%	77.00%

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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

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- Definition

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(2)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

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- Definition

Weighted-average interest crediting rate used to determine benefit obligation of defined benefit plan. Plan includes, but is not limited to, cash balance and other defined benefit plans with promised interest crediting rate.

+ 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)(4)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

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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

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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://fasb.org/us-gaap/role/ref/legacyRef
-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

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- Definition

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(2)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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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://fasb.org/us-gaap/role/ref/legacyRef
-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

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- Definition

Ultimate trend rate for health care cost for defined benefit postretirement plan.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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

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- Definition

Percentage of actual 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/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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