The changes in the carrying amount of goodwill for the six months ended June 30, 2021 and year ended December 31, 2020, are as follows:


(in millions)	Goodwill

Historical goodwill, net of accumulated impairment losses of $10,766	$	1,930
Goodwill from acquisitions in 2020	9,405
Layer3 goodwill impairment	(218)
Balance as of December 31, 2020	11,117

Purchase price adjustment of goodwill from acquisitions in 2020	22
Goodwill from acquisitions in 2021	13

Balance as of June 30, 2021	$	11,152
Accumulated impairment losses at June 30, 2021	$	(10,984)

On April 1, 2020, we completed our Merger with Sprint, which was accounted for as a business combination resulting in $9.4 billion in goodwill. The acquired goodwill was allocated to the wireless reporting unit and will be tested for impairment at this level. See Note 2 - Business Combinations for further information.

The following table summarizes the fair value of the intangible assets acquired in the Merger:


	Weighted Average Useful Life (in years)	Fair Value as of April 1, 2020 (in millions)
Spectrum licenses	Indefinite-lived	$	45,400
Tradenames (1)	2 years	207
Customer relationships	8 years	4,900
Favorable spectrum leases	18 years	745
Other intangible assets	7 years	428
Total intangible assets acquired		$	51,680

Spectrum licenses are issued for a fixed period of time, typically up to 15 years; however, the FCC has granted license renewals routinely and at a nominal cost. The spectrum licenses acquired expire at various dates and we believe we will be able to meet all requirements necessary to secure renewal of our spectrum licenses at a nominal cost. Moreover, we determined that there are currently no legal, regulatory, contractual, competitive, economic or other factors that limit the useful lives of our spectrum licenses. Therefore, we determined the spectrum licenses should be treated as indefinite-lived intangible assets. The fair value of spectrum licenses includes the value associated with aggregating a nationwide portfolio of owned and leased spectrum.

Favorable spectrum leases represent a contract where the market rate is higher than the future contractual lease payments. We lease this spectrum from third parties who hold the spectrum licenses. As these contracts pertain to intangible assets, they are excluded from the lease accounting guidance (ASC 842) and are accounted for as service contracts in which the expense is recognized on a straight-line basis over the lease team. Favorable spectrum leases of $745 million were recorded as an intangible asset as a result of purchase accounting and are amortized on a straight-line basis over the associated remaining lease term. Additionally, we recognized unfavorable spectrum lease liabilities of $125 million, which are also amortized over their respective remaining lease terms and are included in Other liabilities in our Condensed Consolidated Balance Sheets.

The customer relationship intangible assets represent the value associated with the acquired Sprint customers. The customer relationship intangible assets are amortized using the sum-of-the-years’ digits method over periods of up to eight years.

The following table summarizes our spectrum license activity for the six months ended June 30, 2021:


(in millions)	2021
Spectrum licenses, beginning of year	$	82,828

Spectrum license acquisitions	87
Costs to clear spectrum	2

Spectrum licenses, end of period	$	82,917

In March 2021, the FCC announced that we were the winning bidder of 142 licenses in Auction 107 (C-band spectrum) for an aggregate purchase price of $9.3 billion, excluding relocation costs. At the inception of Auction 107 in October 2020, we deposited $438 million. Upon conclusion of Auction 107 in March 2021, we paid the FCC the remaining $8.9 billion for the licenses won in the auction. Cash payments to acquire spectrum licenses and payments for costs to clear spectrum are included in Purchases of spectrum licenses and other intangible assets, including deposits in our Condensed Consolidated Statements of Cash Flows for the three and six months ended June 30, 2021. We expect to incur an additional $1.2 billion in relocation costs which will be paid through 2024.

The aggregate cash payments made to the FCC are included in Other assets as of June 30, 2021, in our Condensed Consolidated Balance Sheets, as the licenses had not yet been issued. As of June 30, 2021, the activities that are necessary to get the C-band spectrum ready for its intended use have not begun, as such, capitalization of the interest associated with the costs of acquiring the C-band spectrum has not begun. Subsequent to June 30, 2021, on July 23, 2021, the FCC issued to us the licenses won in the Auction.

The components of Other intangible assets were as follows:


	Useful Lives	June 30, 2021						December 31, 2020
(in millions)		Gross Amount		Accumulated Amortization		Net Amount		Gross Amount		Accumulated Amortization		Net Amount

Customer relationships	Up to 8 years	$	4,903	$	(1,398)	$	3,505	$	4,900	$	(865)	$	4,035
Tradenames and patents	Up to 19 years	606		(486)		120		598		(412)		186
Favorable spectrum leases	Up to 27 years	741		(54)		687		790		(35)		755
Other	Up to 10 years	377		(89)		288		377		(55)		322

Other intangible assets		$	6,627	$	(2,027)	$	4,600	$	6,665	$	(1,367)	$	5,298

Amortization expense for intangible assets subject to amortization was $295 million and $387 million for the three months ended June 30, 2021 and 2020, respectively, and $661 million and $411 million for the six months ended June 30, 2021 and 2020, respectively.

The estimated aggregate future amortization expense for intangible assets subject to amortization are summarized below:


(in millions)	Estimated Future Amortization

Twelve Months Ending June 30,
2022	$	1,095
2023	903
2024	746
2025	588
2026	428
Thereafter	840

Total	$	4,600