Intangible Assets (Tables)

12 Months Ended

Dec. 31, 2015

Goodwill and Intangible Assets Disclosure [Abstract]

Schedule of intangible assets with definite lives

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

	As of December 31, 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	$	(61	)	$	9	$	70	$	(54	)	$	16
Other	9		(8		)	1		9		(7		)	2
Total	$	79	$	(69	)	$	10	$	79	$	(61	)	$	18

Schedule of estimated annual amortization expense

Estimated annual amortization expense is as follows:

(millions)	2016		2017		2018 and thereafter
Estimated annual amortization expense	$	7	$	2	$	1

Schedule of intangible assets with indefinite lives

Intangible assets with indefinite lives are not amortized. The gross carry amounts of these assets as of December 31 are as follows:

(millions)	2015		2014
Intangible Assets with Indefinite Lives:
Trade names	$	22	$	22
Other	8		8
Total	$	30	$	30