Other Long-Term Assets, Net

Other long-term assets, net of accumulated amortization, consisted of the following (in millions):



	December 31,
	2016			2015
Intangible assets ⁽¹⁾	$	603		$	610
Fair value of derivative instruments	1			9
Other	43			91
	647			710
Accumulated amortization	(361		)	(327		)
	$	286		$	383


⁽¹⁾	We include rights-of-way, which are intangible assets, in our pipeline and related facilities amounts within property and equipment. See Note 5 for a discussion of property and equipment.

Amortization expense for finite-lived intangible assets for the years ended December 31, 2016, 2015 and 2014 was $44 million, $49 million and $57 million, respectively.

Intangible assets that have finite lives are tested for impairment when events or circumstances indicate that the carrying value may not be recoverable. Our intangible assets that have finite lives consisted of the following (in millions):



		December 31, 2016							December 31, 2015
	Estimated Useful Lives (Years)	Cost		Accumulated Amortization			Net		Cost		Accumulated Amortization			Net
Customer contracts and relationships	1 – 20	$	529	$	(330	)	$	199	$	537	$	(301	)	$	236
Property tax abatement	7 – 13	38		(26		)	12		38		(22		)	16
Other agreements	25 – 70	29		(5		)	24		28		(4		)	24
Emission reduction credits ⁽¹⁾	N/A	7		—			7		7		—			7
		$	603	$	(361	)	$	242	$	610	$	(327	)	$	283


⁽¹⁾	Emission reduction credits, once surrendered in exchange for environmental permits, are finite-lived.

We estimate that our amortization expense related to finite-lived intangible assets for the next five years will be as follows (in millions):



2017	$	42
2018	$	37
2019	$	34
2020	$	32
2021	$	30