Employee Benefits - Benefit Obligations Actuarial Assumptions (Details)	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Ultimate health care cost trend rate	4.50%
Minimum
Defined Benefit Plan Disclosure [Line Items]
Initial health care cost trend rate	5.00%
Maximum
Defined Benefit Plan Disclosure [Line Items]
Initial health care cost trend rate	6.25%
Combined Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.43%	3.25%
Rate of compensation increase	3.25%	3.25%
Post-Retirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.40%	3.22%
Ultimate health care cost trend rate	4.50%	4.50%	4.50%
Post-Retirement Benefit Plans | Minimum
Defined Benefit Plan Disclosure [Line Items]
Initial health care cost trend rate	5.00%	5.00%
Post-Retirement Benefit Plans | Maximum
Defined Benefit Plan Disclosure [Line Items]
Initial health care cost trend rate	6.25%	6.50%