New Accounting Pronouncements (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($)	Sep. 30, 2017 USD ($) aircraft
New Accounting Pronouncements or Change in Accounting Principle
Aircraft under operating lease | aircraft		53
Net Present Value Aircraft Operating Leases		$ 1,000
Rapid Rewards Frequent Flier Liability		$ 64
Reclassification From Other Revenue Into Passenger Revenue Related to the Adoption of Topic 606 of the New Revenue Recognition Standard	$ 600
Minimum
New Accounting Pronouncements or Change in Accounting Principle
Estimated Impact		20
Maximum
New Accounting Pronouncements or Change in Accounting Principle
Estimated Impact		25
B-717-200
New Accounting Pronouncements or Change in Accounting Principle
Aircraft under operating lease | aircraft		76