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Pension and Other Postretirement Benefit Plans - Summary of Health Care Cost Trend Rate Assumptions for Other Postretirement Benefit Plans (Details) - Other Postretirement Benefits
Dec. 31, 2020
Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]    
Health care cost trend rate assumed for next year 6.60% 6.80%
Rate to which the cost trend rate is assumed to decline 4.50% 4.50%