Employee Benefit Plans - Assumptions Used to Determine Benefit Obligation and Net Periodic Benefit Cost (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure
Weighted average discount rate (percent)	2.62%	3.40%
Weighted average expected long-term rate of return on plan assets (percent)	8.97%	8.97%	8.97%
Assumed healthcare cost trend rate for the next year (percent)	6.25%	6.50%	6.75%
Ultimate healthcare cost trend rate (percent)	5.00%
Pension Benefits
Defined Benefit Plan Disclosure
Weighted average discount rate (percent)	3.40%	4.33%	3.69%
Other Postretirement Benefits
Defined Benefit Plan Disclosure
Weighted average discount rate (percent)	3.47%	4.32%	3.69%
Other Postemployment Benefits
Defined Benefit Plan Disclosure
Weighted average discount rate (percent)	3.34%	4.32%	3.65%