The following table sets forth the changes in the carrying amount of the Company’s goodwill, net by segment for the years ended December 31, 2020 and 2019.

	December 31,
	2020		2019
Titanium Technologies:
Balance at January 1,	$	13	$	13
Balance at December 31,		13		13
Thermal & Specialized Solutions:
Balance at January 1,		33		33
Balance at December 31,		33		33
Advanced Performance Materials:
Balance at January 1,		56		56
Balance at December 31,		56		56
Chemical Solutions:
Balance at January 1,		51		51
Balance at December 31,		51		51
Total goodwill, net	$	153	$	153

Chemours consists of four operating segments: Titanium Technologies, Thermal & Specialized Solutions, Advanced Performance Materials, and Chemical Solutions. The Company’s reporting units are consistent with its operating segments, with the exception of the Chemical Solutions segment, which is comprised of the Mining Solutions and Performance Chemicals and Intermediates reporting units. For the years ended December 31, 2020 and 2019, the Company did not have any adjustments to or transfers of its goodwill balances, which are recorded in U.S. dollars. The Company tested the goodwill balances attributable to each of its reporting units for potential impairment on October 1, 2020 and 2019, the dates of Chemours’ annual goodwill assessment. No goodwill impairments were recorded for the years ended December 31, 2020 and 2019, as the fair values of the Company’s reporting units that carry goodwill exceeded each respective reporting unit’s carrying amount on October 1, 2020 and 2019.

The total accumulated impairment losses included in the Company’s goodwill, net balance at December 31, 2020 and 2019 amounted to $4.

The following table sets forth the gross carrying amounts and accumulated amortization of the Company’s other intangible assets by major class at December 31, 2020 and 2019.

	December 31, 2020							December 31, 2019
	Cost		Accumulated Amortization			Net		Cost		Accumulated Amortization			Net
Customer lists	$	9	$	(9	)	$	—	$	9	$	(8	)	$	1
Customer relationships		22		(12	)		10		22		(8	)		14
Patents		19		(19	)		—		19		(19	)		—
Purchased trademarks		5		(3	)		2		5		(3	)		2
Purchased and licensed technology		3		(3	)		—		3		(3	)		—
Other (1)		10		(8	)		2		10		(6	)		4
Total other intangible assets	$	68	$	(54	)	$	14	$	68	$	(47	)	$	21

The aggregate pre-tax amortization expense for definite-lived intangible assets was $7, $7, and $6 for the years ended December 31, 2020, 2019, and 2018, respectively. The estimated aggregate pre-tax amortization expense for 2021, 2022, 2023, 2024, and 2025 is $7, $5, $1, less than $1, and less than $1, respectively. Definite-lived intangible assets are amortized over their estimated useful lives, generally for periods ranging from five to 20 years. The reasonableness of the useful lives of these assets is periodically evaluated. The Company does not have any indefinite-lived intangible assets.