Intangible Assets

12 Months Ended

Dec. 31, 2019

Goodwill and Intangible Assets Disclosure [Abstract]

Intangible Assets

INTANGIBLE ASSETS

Indefinite-Lived Intangible Assets

	Carrying Value at December 31,
(in millions)	2019		2018
International routes and slots	$	2,583	$	2,583
Airline alliances	1,005		661
Delta tradename	850		850
Domestic slots	622		622
Total	$	5,060	$	4,716

International Routes and Slots. Our international routes and slots primarily relate to Pacific route authorities and slots at capacity-constrained airports in Asia, and slots at London-Heathrow airport.

Airline Alliances. Our airline alliances intangible assets primarily relate to our commercial agreements with SkyTeam partners and LATAM.

Domestic Slots. Our domestic slots relate to our slots at New York-LaGuardia and Washington-Reagan National airports.

Definite-Lived Intangible Assets

	December 31, 2019				December 31, 2018
(in millions)	Gross Carrying Value		Accumulated Amortization		Gross Carrying Value		Accumulated Amortization
Marketing agreements	$	730	$	(692)	$	730	$	(687)
Contracts	193		(128)		193		(122)
Other	53		(53)		53		(53)
Total	$	976	$	(873)	$	976	$	(862)

Amortization expense was $11 million for the year ended December 31, 2019 and $17 million for each of the years ended December 31, 2018 and 2017. Based on our definite-lived intangible assets at December 31, 2019, we estimate that we will incur approximately $9 million of amortization expense annually from 2020 through 2024.