(6) Goodwill and Other Intangibles:

We are required to perform impairment tests related to our goodwill annually, which we perform as of December 31, or sooner if an indicator of impairment occurs. During our quarterly qualitative assessment, we determined it was more likely than not that the fair value of our operating segment was less than the carrying amount, and as a result of that assessment, we tested goodwill for impairment as of September 30, 2018.

We use a market multiples approach to determine fair value. Marketplace company comparisons and analyst reports within the telecommunications industry have historically supported a range of fair values of multiples between 5.0x and 7.9x annualized EBITDA (defined as operating income, net of acquisition and integration costs, noncash pension and OPEB costs, pension settlement costs, goodwill impairment and restructuring costs and other charges, as well as depreciation and amortization). We estimated the enterprise fair value using a multiple of 5.5x EBITDA.

Our quantitative assessment indicated that the carrying value of the enterprise exceeded its fair value and, therefore, an impairment existed. We recorded goodwill impairment of $400 million, which was based on the amount that the enterprise carrying value exceeded the fair value.

The market multiples approach that we use incorporates significant estimates and assumptions related to the forecasted results for the remainder of the year including revenues, expenses, and the achievement of other cost synergies. Our assessment includes many qualitative factors that require significant judgment. Alternative interpretations of these factors could have resulted in different conclusions regarding the need for, or size of, an impairment. Continued declines in our profitability or cash flows or in the trading value of our common stock may result in further impairment.

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, noting no additional impairment was present as of September 30, 2018.

Total accumulated goodwill impairments were $3,188 million and $2,788 million as of September 30, 2018 and December 31, 2017, respectively.

The components of other intangibles are as follows:


	September 30, 2018						December 31, 2017
	Gross Carrying		Accumulated		Net Carrying		Gross Carrying		Accumulated		Net Carrying
($ in millions)	Amount		Amortization		Amount		Amount		Amortization		Amount

Other Intangibles:
Customer base	$	5,188	$	(3,721)	$	1,467	$	5,188	$	(3,294)	$	1,894
Trade name		122		-		122		122		-		122
Royalty agreement		72		(35)		37		72		(25)		47
Total other intangibles	$	5,382	$	(3,756)	$	1,626	$	5,382	$	(3,319)	$	2,063

Amortization expense was as follows:


	For the three months ended September 30,				For the nine months ended September 30,
($ in millions)	2018		2017		2018		2017

Amortization expense	$	134	$	163	$	437	$	539

Amortization expense primarily represents the amortization of our customer base acquired as a result of our acquisitions in 2010, 2014, and 2016 with each based on a useful life of 8 to 12 years on an accelerated method.