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Pension Plan and Other Postretirement Benefits - Pension Plan Asset Allocations by Asset Category (Details) - Pension Plan	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Asset Allocation	100.00%	100.00%
Global MGD Volatility Fund (mixed equities fund)
Defined Benefit Plan Disclosure [Line Items]
Asset Allocation	19.30%	20.40%
Large Capitalization Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Asset Allocation	11.80%	11.30%
International Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Asset Allocation	9.90%	9.30%
Emerging Markets Equity Fund
Defined Benefit Plan Disclosure [Line Items]
Asset Allocation	4.50%	4.20%
Small and Mid-Capitalization Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Asset Allocation	4.50%	4.10%
SEI Dynamic Asset Allocation Fund
Defined Benefit Plan Disclosure [Line Items]
Asset Allocation	3.20%	3.10%
Equity
Defined Benefit Plan Disclosure [Line Items]
Asset Allocation	53.20%	52.40%
Fixed-Income Securities and Cash
Defined Benefit Plan Disclosure [Line Items]
Asset Allocation	44.20%	44.70%
Other – SEI Energy Debt Collective Fund
Defined Benefit Plan Disclosure [Line Items]
Asset Allocation	2.60%	2.90%

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- Definition

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+ References

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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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