Note 7—Other Assets, Net

Other assets, net of accumulated amortization, consist of the following (in millions):

	December 31,
	2012			2011
Debt issue costs	$	69		$	53
Fair value of derivative instruments	10			20
Intangible assets	642			498
Other	54			59
	775			630
Accumulated amortization	(189		)	(84		)
	$	586		$	546

Costs incurred in connection with the issuance of long-term debt and amendments to our credit facilities are capitalized and amortized using the straight-line method over the term of the related debt. Use of the straight-line method does not differ materially from the “effective interest” method of amortization. Fully amortized debt issue costs and the related accumulated amortization are written off in conjunction with the refinancing or termination of the applicable debt arrangement. We capitalized debt issue costs of approximately $20 million and $18 million in 2012 and 2011, respectively. Approximately $5 million and $11 million of gross debt issue costs were removed from our Consolidated Balance Sheet during 2012 and 2011, respectively, primarily related to the restructuring of our credit facilities in June 2012 and August 2011.

Amortization expense related to other assets (including finite-lived intangible assets) for the three years ended December 31, 2012, 2011 and 2010 was approximately $110 million, $44 million and $22 million, respectively. Our amortization expense for finite-lived intangible assets for the years ended December 31, 2012, 2011 and 2010 was approximately $101 million, $36 million and $14 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 consist of the following (in millions):

		December 31, 2012							December 31, 2011
	Estimated Useful			Accumulated								Accumulated
	Lives (Years)	Cost		Amortization			Net			Cost		Amortization			Net
Customer contracts and relationships	1 - 20	$	558	$	(157	)	$	401		$	426	$	(61	)	$	365
Property tax abatement	7 - 13	38		(10		)	28			38		(6		)	32
Other agreements	25 - 70	38		(2		)	36			26		(1		)	25
Emission reduction credits (1)	N/A	8		—			8			8		—			8
		$	642	$	(169	)	$	473		$	498	$	(68	)	$	430

(1) Emission reduction credits are finite-lived and are subject to surrender in exchange for environmental permits.

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

2013	$	78
2014	$	53
2015	$	48
2016	$	42
2017	$	40