Commitments and Contingencies - Airport Projects (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2010	Dec. 31, 2017
Airport Project [Line Items]
Reimbursement for airport construction		$ 139	$ 49
Assets constructed for others		1,607			$ 1,543
Assets constructed for others, net		1,504			1,448
Construction obligation		1,563			1,390
Fort Lauderdale-Hollywood International Airport
Airport Project [Line Items]
Total Expected Cost Of Airport Project		333
Assets constructed for others	[1]	282			258
Assets constructed for others, net	[1],[2]	279			256
Construction obligation	[1],[3]	281			258
Los Angeles World Airport Terminal 1
Airport Project [Line Items]
Total Expected Cost Of Airport Project		526
Total Expected Cost Of Airport Project Nonproprietary		510
Remaining guaranteed obligation		143
Assets constructed for others	[1]	450			433
Assets constructed for others, net	[1],[2]	432			417
Construction obligation	[1],[3]	447			433
Los Angeles World Airport Terminal 1.5
Airport Project [Line Items]
Total Expected Cost Of Airport Project		479
Remaining guaranteed obligation		46
Assets constructed for others	[1]	42			31
Assets constructed for others, net	[1],[2]	42			31
Construction obligation	[1],[3]	42			31
Dallas Love Field Terminal
Airport Project [Line Items]
Assets constructed for others		543			543
Assets constructed for others, net	[2]	470			474
Construction obligation	[3]	513			516
Municipal bonds issued				$ 456
Municipal bonds principal remaining		424
Dallas Love Field Parking Garage
Airport Project [Line Items]
Assets constructed for others	[1]	164			152
Assets constructed for others, net	[1],[2]	164			152
Construction obligation	[1],[3]	164			152
Houston Hobby Airport
Airport Project [Line Items]
Total Cost of Airport Project		150
Reimbursement for airport construction		116
Assets constructed for others		126			126
Assets constructed for others, net	[2]	117			118
Construction obligation	[3]	$ 116			$ 0

[1] Projects still in progress.

[2] Net of accumulated depreciation.

[3] Construction obligation will be reduced through future facility rent payments. These future payments are not fixed per the lease agreement, but are variable and fluctuate based on various market and other factors outside the control of the Company.