Intangible Assets (Tables)

12 Months Ended

Dec. 31, 2012

Goodwill and Intangible Assets Disclosure [Abstract]

Schedule of Finite-Lived Intangible Assets

Intangible assets with definite lives are amortized. These assets are summarized as follows:

	As of December 31, 2012							As of December 31, 2011
(millions)	Gross Carrying Amount		Accumulated Amortization			Net		Gross Carrying Amount		Accumulated Amortization			Net
Intangible Assets with Definite Lives:
Customer relationships	$	70	$	(41	)	$	29	$	70	$	(34	)	$	36
Other	9		(6		)	3		9		(5		)	4
Total	$	79	$	(47	)	$	32	$	79	$	(39	)	$	40

Estimated Annual Amortization Expense Intangible Assets

Estimated annual amortization expense is as follows:

(millions)	2013		2014		2015		2016		2017 and thereafter
Estimated annual amortization expense	$	7	$	7	$	7	$	7	$	4

Schedule of Indefinite-Lived Intangible Assets

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

	As of December 31, 2012						As of December 31, 2011
(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