Pension and Other Post-Retirement Benefits - Assumed Health Care Cost Trend Rates (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Health Care Cost Trend Rate Assumed for Next Fiscal Year, Post Age 65	5.63%	5.60%
Medical Claims [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Health Care Cost Trend Rate Assumed for Next Fiscal Year, Pre Age 65	6.44%	6.40%
Review of historical returns
Rate to which the cost trend is expected to decline (the ultimate trend rate)	4.50%
Year that rate reaches the ultimate trend rate	2028	2028
Prescription Drugs Claims [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Health Care Cost Trend Rate Assumed for Next Fiscal Year, Pre Age 65	8.78%	8.80%
Defined Benefit Plan, Health Care Cost Trend Rate Assumed for Next Fiscal Year, Post Age 65	8.63%	8.60%
Review of historical returns
Rate to which the cost trend is expected to decline (the ultimate trend rate)	4.50%
Year that rate reaches the ultimate trend rate	2028	2028