Pension and Postretirement Benefits - Weighted-Average Assumptions Used to Determine Projected Benefit Obligations and Periodic Benefit Cost (Details)	1 Months Ended	12 Months Ended
	Feb. 07, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate for determining projected benefit obligation at December 31	3.57%	2.00%	2.79%	3.86%
Discount rate in effect for determining service cost	3.16%	2.11%	3.11%	2.99%
Discount rate in effect for determining interest cost	3.51%	2.48%	3.29%	2.90%
Weighted average expected long-term return on plan assets	6.56%	6.19%	6.72%	6.72%
Rate of compensation increase for determining projected benefit obligation at December 31	3.00%	3.00%	3.00%	2.99%
Rate of compensation increase for determining net pension cost	3.04%	3.00%	3.07%	6.10%
Postretirement Benefit Obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate for determining projected benefit obligation at December 31	3.64%	1.20%	2.35%	3.88%
Discount rate in effect for determining service cost				3.15%
Discount rate in effect for determining interest cost	3.52%	2.10%	3.25%	2.85%