Intangible Assets

6 Months Ended

Jun. 30, 2015

Goodwill and Intangible Assets Disclosure [Abstract]

Intangible assets are included in other assets on our accompanying consolidated balance sheets. Intangible assets with definite lives are amortized. These assets are summarized as follows:



	As of June 30, 2015							As of December 31, 2014
(millions)	Gross Carrying Amount		Accumulated Amortization			Net		Gross Carrying Amount		Accumulated Amortization			Net
Intangible Assets with Definite Lives:
Customer relationships	$	70	$	(58	)	$	12	$	70	$	(54	)	$	16
Other	9		(7		)	2		9		(7		)	2
Total	$	79	$	(65	)	$	14	$	79	$	(61	)	$	18

Total amortization expense was $2 million and $4 million for the three and six months ended June 30, 2015 and 2014, respectively. Estimated amortization expense for the remainder of 2015 and for future years is as follows:



(millions)	2015		2016		2017		2018 and thereafter
Estimated future amortization expense	$	4	$	7	$	2	$	1

Intangible assets with indefinite lives are not amortized. These assets are summarized as follows:



	As of June 30, 2015							As of December 31, 2014
(millions)	Gross Carrying Amount		Accumulated Impairment Charges			Net		Gross Carrying Amount		Accumulated Impairment Charges			Net
Intangible Assets with Indefinite Lives:
Trade names	$	22	$	—		$	22	$	22	$	—		$	22
Other	9		(1		)	8		9		(1		)	8
Total	$	31	$	(1	)	$	30	$	31	$	(1	)	$	30

As of December 31, 2014, approximately $5 million of other indefinite-lived intangible assets met the criteria to be classified as held for sale and therefore were included in other current assets on our accompanying consolidated balance sheet. As of June 30, 2015, these indefinite-lived intangible assets were no longer recorded as held for sale.