Employee and Retiree Benefit Plans - Weighted-Average Assumptions used in Measurement of Benefit Obligations and Net Periodic Benefit Expense (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets	4.70%
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Benefit obligations, discount rate	2.25%	3.85%
Net periodic benefit expense, discount rate	2.75%	3.35%
Expected return on plan assets	4.43%	5.05%
Benefit obligation, rate of compensation increase	3.04%	3.28%
Net periodic benefit expense, rate of compensation increase	3.28%	3.52%
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Benefit obligations, discount rate	2.50%	3.42%
Net periodic benefit expense, discount rate	3.16%	4.42%
Expected return on plan assets	0.00%	0.00%
Benefit obligation, rate of compensation increase	0.00%	0.00%
Net periodic benefit expense, rate of compensation increase	0.00%	0.00%