Pension and Other Post-Retirement Benefit Plans (Schedule of Assumptions) (Details)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Plans [Member]
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Expected return on plan assets	6.25%	6.25%	6.25%
Crewmembers [Member] | Pension Plans [Member]
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate	4.00%	4.50%	4.70%
Non-crewmembers [Member] | Pension Plans [Member]
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate	4.05%	4.60%	4.75%
Pilots [Member] | Post-Retirement Healthcare Plans [Member]
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate	3.30%	3.55%	3.65%
Non-pilots [Member] | Post-Retirement Healthcare Plans [Member]
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate			3.35%