Pension and Other Postretirement Benefit Plans - Retirement Plan Weighted Average Asset Allocations (Details) - Retirement Plan [Member]	Dec. 31, 2020	Dec. 31, 2019
Equity Securities [Member]
Weighted average asset allocation	0.00%	0.00%
Debt Securities [Member]
Weighted average asset allocation	100.00%	100.00%

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.

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

Name:	us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant