Commitments and Contingencies - Airport Projects (Details) - USD ($) $ in Millions		Mar. 31, 2019	Dec. 31, 2018
Other Commitments [Line Items]
ACFO		$ 120	$ 1,768
Assets constructed for others, net		120	1,637
Construction Obligation		120	1,701
FLL Terminal
Other Commitments [Line Items]
ACFO		0	313
Assets constructed for others, net	[1]	0	304
Construction Obligation		0	308
LAX Terminal 1
Other Commitments [Line Items]
Outstanding remaining guaranteed obligation		111
ACFO		0	485
Assets constructed for others, net	[1]	0	459
Construction Obligation		0	476
LAX Terminal 1.5
Other Commitments [Line Items]
Total Expected Cost Of Airport Project		479
Outstanding remaining guaranteed obligation		125
ACFO	[2]	120	99
Assets constructed for others, net	[1],[2]	120	99
Construction Obligation	[2]	120	99
LFMP Terminal
Other Commitments [Line Items]
ACFO		0	545
Assets constructed for others, net	[1]	0	460
Construction Obligation		0	502
Municipal bonds principal remaining		416
Net present value of principal remaining		459
LFMP Parking Garage
Other Commitments [Line Items]
ACFO		0	200
Assets constructed for others, net	[1]	0	200
Construction Obligation		0	200
HOU International Terminal
Other Commitments [Line Items]
ACFO	[3]	0	126
Assets constructed for others, net	[1],[3]	0	115
Construction Obligation	[3]	$ 0	$ 116

[1] Net of accumulated depreciation.

[2] Project still in progress.

[3] Project completed in 2015 at Houston William P. Hobby Airport ("HOU").