Intangible Assets (Tables)

6 Months Ended

Jun. 30, 2013

Goodwill and Intangible Assets Disclosure [Abstract]

Intangible assets with definitive lives

These assets are summarized as follows:

	As of June 30, 2013							As of December 31, 2012
(millions)	Gross Carrying Amount		Accumulated Amortization			Net		Gross Carrying Amount		Accumulated Amortization			Net
Intangible Assets with Definite Lives:
Customer relationships	$	70	$	(45	)	$	25	$	70	$	(41	)	$	29
Other	9		(6		)	3		9		(6		)	3
Total	$	79	$	(51	)	$	28	$	79	$	(47	)	$	32

Estimated annual amortization expense intangible assets

Estimated amortization expense for the remainder of 2013 and for future years is as follows:

(millions)	2013		2014		2015		2016		2017		2018 and thereafter
Estimated future amortization expense	$	4	$	7	$	7	$	7	$	2	$	1

Schedule of indefinite-lived intangible assets

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

	As of June 30, 2013						As of December 31, 2012
(millions)	Gross Carrying Amount		Impairment Charges		Net		Gross Carrying Amount		Impairment Charges		Net
Intangible Assets with Indefinite Lives:
Trade names	$	22	$	—	$	22	$	22	$	—	$	22
Other	8		—		8		8		—		8
Total	$	30	$	—	$	30	$	30	$	—	$	30