Intangible Assets

6 Months Ended

Jun. 30, 2021

Goodwill and Intangible Assets Disclosure [Abstract]

Intangible Assets

9.     Intangible Assets and Goodwill

Intangible assets that are being amortized on a straight-line basis over their estimated useful lives are detailed below:

		As of June 30, 2021						As of December 31, 2020
(In millions)	Useful Lives	Gross Carrying Amount		Accumulated Amortization		Net Amount		Gross Carrying Amount		Accumulated Impairment		Accumulated Amortization		Net Amount
Customer relationships	22 Years	$	413	$	9	$	404	$	132	$	55	$	77	$	—
Patents	10-15 Years	17		10		7		22		7		10		5
Energy Contract	10 Years	54		7		47		54		—		5		49
Other	4-20 Years	—		—		—		14		5		9		—
Total amortizable intangible assets		$	484	$	26	$	458	$	222	$	67	$	101	$	54

Total estimated amortization expense for the remainder of 2021 is $13 million. We expect approximately $25 million in annual amortization expense through 2026 and approximately $320 million in remaining amortization expense thereafter.

The carrying amount of acquired water rights with indefinite lives as of June 30, 2021 and December 31, 2020 totaled $75 million.

Below is a summary of goodwill by segment for the six months ended June 30, 2021:

	Flat-Rolled		Mini Mill		USSE		Tubular		Total
Balance at December 31, 2020	$	—	$	—	$	4	$	—	$	4
Additions	—		905		—		—		905
Balance at June 30, 2021	$	—	$	905	$	4	$	—	$	909