Intangible assets

9 Months Ended

Sep. 30, 2021

Intangible assets

Intangible assets

8. INTANGIBLE ASSETS

	September 30, 2021						December 31, 2020
	Gross carrying value		Accumulated amortization		Net carrying value		Gross carrying value		Accumulated amortization		Net carrying value
Customer relationships	$	615	$	(179)	$	436	$	615	$	(146)	$	469
Technologies		367		(260)		107		369		(211)		158
Software		366		(155)		211		298		(125)		173
Backlog		129		(104)		25		129		(79)		50
Image library		80		(68)		12		80		(58)		22
Trade names and other		37		(16)		21		38		(15)		23
Intangible assets	$	1,594	$	(782)	$	812	$	1,529	$	(634)	$	895

Amortization expense related to intangible assets was $51 million and $71 million for the three months ended September 30, 2021 and 2020, respectively, and $154 million and $203 million for the nine months ended September 30, 2021 and 2020, respectively.