Note 3. Goodwill and Intangible Assets

Goodwill

The changes in the carrying amount of goodwill by segment are as follows:


(In millions)		Textron Aviation		Bell		Textron Systems		Industrial		Total
Balance at December 31, 2016	$	613	$	31	$	1,087	$	382	$	2,113
Acquisitions		—		—		—		234		234
Foreign currency translation		1		—		—		16		17

Balance at December 30, 2017		614		31		1,087		632		2,364
Disposition		—		—		—		(153)		(153)
Acquisition		—		—		13		—		13
Foreign currency translation		—		—		—		(6)		(6)

Balance at December 29, 2018	$	614	$	31	$	1,100	$	473	$	2,218

Intangible Assets

Our intangible assets are summarized below:


		December 29, 2018						December 30, 2017
(Dollars in millions)	Weighted-Average Amortization Period (in years)		Gross Carrying Amount		Accumulated Amortization		Net		Gross Carrying Amount		Accumulated Amortization		Net

Patents and technology	14	$	514	$	(211)	$	303	$	545	$	(188)	$	357
Trade names and trademarks	14		224		(7)		217		284		(40)		244
Customer relationships and contractual agreements	15		413		(275)		138		418		(255)		163
Other	4		6		(6)		—		18		(17)		1

Total		$	1,157	$	(499)	$	658	$	1,265	$	(500)	$	765

In connection with the 2018 restructuring plan discussed in Note 15, we recognized intangible asset impairment charges of $38 million in the fourth quarter of 2018, which primarily included $20 million of patents and technology and $14 million of trade names and trademarks.

Trade names and trademarks in the table above include $208 million and $222 million of indefinite-lived intangible assets at December 29, 2018 and December 30, 2017, respectively. Amortization expense totaled $66 million, $69 million and $66 million in 2018, 2017 and 2016, respectively. Amortization expense is estimated to be approximately $60 million, $56 million, $54 million, $54 million and $38 million in 2019, 2020, 2021, 2022 and 2023, respectively.