Other Intangible Assets and Liabilities

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



	As of June 30, 2015				As of December 31, 2014
	Gross Carrying Amount		Accumulated Amortization		Gross Carrying Amount		Accumulated Amortization
Intangible assets	$	647	$	173	$	2,031	$	1,519
Intangible liabilities	$	1,403	$	682	$	2,056	$	1,274

As of June 30, 2015, intangible assets primarily consisted of franchise and customer assets. At December 31, 2014, intangible assets also included internally developed software that became fully amortized in the first quarter of 2015. 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):



	Six Months Ended June 30,
	2015		2014
Amortization of intangible assets	$	39	$	155
Amortization of intangible liabilities	$	61	$	89

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 2015	$	17	$	54
2016	$	34	$	101
2017	$	33	$	96
2018	$	31	$	90
2019	$	31	$	27