Pension and Postretirement Benefits - Healthcare Trend Assumptions (Details)	Dec. 31, 2027	Dec. 31, 2020
Forecast
Defined Benefit Plan Disclosure [Line Items]
Ultimate health care cost trend rate (as a percent)	5.00%
Medical
Defined Benefit Plan Disclosure [Line Items]
Ultimate health care cost trend rate (as a percent)		5.30%
Prescription drug
Defined Benefit Plan Disclosure [Line Items]
Ultimate health care cost trend rate (as a percent)		8.50%