Other Intangible Assets and Liabilities

Intangible assets and liabilities were as follows (in millions):



	As of September 30, 2014				As of December 31, 2013
	Gross Carrying Amount		Accumulated Amortization		Gross Carrying Amount		Accumulated Amortization
Intangible assets	$	2,031	$	1,442	$	2,030	$	1,209
Intangible liabilities	$	2,056	$	1,229	$	2,056	$	1,095

Intangible assets primarily consisted of internally developed software and franchise and customer assets. Intangible liabilities primarily consisted of customer and shortline contracts which were in an unfavorable position at the date of Merger.

Amortizable intangible assets and liabilities are amortized based on the estimated pattern in which the economic benefits are expected to be consumed or on a straight-line basis over their estimated economic lives.

Amortization of intangible assets and liabilities was as follows (in millions):



	Nine Months Ended September 30,
	2014		2013
Amortization of intangible assets	$	233	$	229
Amortization of intangible liabilities	$	134	$	189

Amortization of intangible assets and liabilities for the next five years is expected to approximate the following (in millions):



	Amortization of intangible assets		Amortization of intangible liabilities
Remainder of 2014	$	77	$	45
2015	$	56	$	115
2016	$	33	$	101
2017	$	33	$	96
2018	$	31	$	90