Pension and Other Post-Retirement Benefit Plans (Schedule of Assumptions) (Details)	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Plans [Member]
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Expected return on plan assets	5.75%	6.10%	6.20%
Crewmembers [Member] | Pension Plans [Member]
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate	2.55%	3.65%	4.65%
Non-crewmembers [Member] | Pension Plans [Member]
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate	2.75%	3.70%	4.65%
Pilots [Member] | Post-Retirement Healthcare Plans [Member]
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate	1.30%	2.60%	4.10%