($ in millions)	Goodwill, net

Balance at January 1, 2018	$	7,024
Goodwill Impairment		(641	)
Balance at December 31, 2018		6,383
Reclassified as held for sale ⁽¹⁾		(658	)
Goodwill impairment		(5,725	)
Balance at December 31, 2019	$	-

We perform impairment tests related to our goodwill annually as of December 31, or sooner if an indicator of impairment occurs. Accumulated goodwill impairment charges were $9,154 million and $3,429 million as of December 31, 2019 and 2018, respectively.

The decline in our stock price, our profitability, and the outlook of our business during the second and third quarter of 2019 were each triggering events that required an impairment assessment in each of the second and third quarter of 2019. The decline of our stock price during 2018 was a triggering event that required an impairment assessment in each of the final three quarters of 2018. As of September 30, 2019, goodwill was fully impaired and therefore no qualitative or quantitative assessment was required as of December 31, 2019.

We use a market multiples approach to determine Frontier’s enterprise fair value for purposes of assessing goodwill for impairment. Marketplace comparisons, analyst reports and trends for other public companies within the communications industry whose service offerings are comparable to ours have a range of fair value multiples between 4.4x and 6.5x of annualized expected EBITDA as adjusted for certain items. We estimated the enterprise fair value using a multiple of 4.4x EBITDA for both the second and third quarter 2019 evaluations, a multiple of 5.3x EBITDA for the fourth quarter 2018 evaluation, and a multiple of 5.5x EBITDA for each of the first three quarterly evaluations in 2018.

The market multiples approach we use incorporates significant estimates and assumptions related to our forecasted profitability, principally revenue and operating expenses. Our assessment also includes certain qualitative factors that required significant judgment, including challenges in achieving improvements in revenue and customer trends, the amount and timing of other anticipated Transformation benefits, and uncertainty regarding the timing and successor to the FCC’s CAF Phase II program. Alternative interpretations of these factors could have resulted in different conclusions regarding the need for, or size of, an impairment.

We recorded goodwill impairments totaling $5,725 million for the year ended December 31, 2019. The impairment in the second and third quarters of 2019 reflected lower enterprise valuation driven by lower profitability, as well as a reduction in the utilized market multiple from 5.3x EBITDA at December 31, 2018 to the 4.4x EBITDA utilized during our quantitative assessments in 2019. This reflects, among other things, pressures on our business resulting in the continued deterioration in revenue, challenges in achieving improvements in revenue and customer trends, the long-term sustainability of our capital structure, and the lower outlook of our industry as a whole.

We recorded goodwill impairments totaling $641 million for year ended December 31, 2018. The driver for the impairment in the third quarter of 2018 was a reduction in our profitability and utilized EBITDA estimate, which when applied to our market multiple resulted in a lower enterprise valuation. During the fourth quarter of 2018, the impairment was largely driven by a lower enterprise valuation resulting from a reduction in utilized market multiple from 5.5x to 5.3x reflecting the lower outlook for our industry as a whole.

We recorded goodwill impairments totaling $2,748 million for the year ended December 31, 2017. The driver for the impairment in the second quarter of 2017 was a reduction in our profitability and utilized EBITDA estimate, which when applied to our market multiple resulted in a lower enterprise valuation. During the fourth quarter, the impairment was largely driven by a lower enterprise valuation resulting from a reduction in utilized market multiple from 5.8x to 5.5x reflecting the lower outlook for our industry as a whole. The revaluation of our net deferred tax liabilities which resulted from the enactment of Tax Cut and Job Act, caused further goodwill impairment (see Note 15).

We also considered whether the carrying values of finite-lived intangible assets and property plant and equipment may not be recoverable or whether the carrying value of certain indefinite-lived intangible assets were impaired. No impairment was present for either finite-lived intangibles or property plant and equipment as of December 31, 2019, 2018, and 2017.

	2019							2018
($ in millions)	Gross Carrying Amount		Accumulated Amortization			Net Carrying Amount		Gross Carrying Amount		Accumulated Amortization			Net Carrying Amount

Other Intangibles:
Customer base	$	4,332	$	(3,452	)	$	880	$	5,188	$	(3,848	)	$	1,340
Trade name		122		-			122		122		-			122
Royalty agreement		72		(54	)		18		72		(40	)		32
Total other intangibles	$	4,526	$	(3,506	)	$	1,020	$	5,382	$	(3,888	)	$	1,494

The decrease in our customer base was driven by the reclassification of $856 million ($30 million net of accumulated amortization) related to the customer base asset expected to be transferred in the planned divestiture of our Northwest Operations.

Amortization expense primarily represents the amortization of our customer base acquired as a result of the CTF Acquisition, the Connecticut Acquisition and the acquisition of certain Verizon properties in 2010 with each based on a useful life of 8 to 12 years on an accelerated method. The approximate weighted average remaining life of our customer base is 4.4 years and for our royalty agreement is 1.3 years. Amortization expense based on our current estimate of useful lives, is estimated to be approximately $343 million in 2020, $253 million in 2021, $170 million in 2022, $95 million in 2023, and $26 million in 2024.