Benefit Plans - Assumed Health Care Cost Trend Rate (Details) - Other Postretirement Benefits	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan, Assumed Health Care Cost Trend Rates [Abstract]
Healthcare cost trend rate assumed for next year (as a percent)	6.30%	7.10%	7.90%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate) (as a percent)	4.70%	7.10%	7.90%

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.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-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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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant