Employee Benefits - Benefit Obligations Actuarial Assumptions (Details)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
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	6.50%
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.25%	4.29%
Rate of compensation increase	3.25%	3.25%
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.22%	4.26%
Ultimate health care cost trend rate	4.50%	4.50%	4.50%
Other Postretirement Benefits Plan | Minimum
Defined Benefit Plan Disclosure [Line Items]
Initial health care cost trend rate	5.00%	5.00%
Other Postretirement Benefits Plan | Maximum
Defined Benefit Plan Disclosure [Line Items]
Initial health care cost trend rate	6.50%	7.00%