Segment information

We operate in one business segment: human therapeutics. Therefore, results of our operations are reported on a consolidated basis for purposes of segment reporting, consistent with internal management reporting. Enterprise-wide disclosures about product sales; revenues and long-lived assets by geographic area; and revenues from major customers are presented below.

Revenues

Revenues were as follows (in millions):



	Years ended December 31,
	2017		2016		2015
Product sales:
ENBREL	$	5,433	$	5,965	$	5,364
Neulasta^®	4,534		4,648		4,715
Aranesp^®	2,053		2,093		1,951
Prolia^®	1,968		1,635		1,312
Sensipar^®/Mimpara^®	1,718		1,582		1,415
XGEVA^®	1,575		1,529		1,405
EPOGEN^®	1,096		1,282		1,856
KYPROLIS^®	835		692		512
Vectibix^®	642		611		549
Nplate^®	642		584		525
NEUPOGEN^®	549		765		1,049
Repatha^®	319		141		10
BLINCYTO^®	175		115		77
Other	256		250		204
Total product sales	21,795		21,892		20,944
Other revenues	1,054		1,099		718
Total revenues	$	22,849	$	22,991	$	21,662

Geographic information

Outside the United States, we sell products principally in Europe. The geographic classification of product sales is based on the location of the customer. The geographic classification of all other revenues is based on the domicile of the entity from which the revenues were earned.

Certain geographic information with respect to revenues and long-lived assets (consisting of property, plant and equipment, net) was as follows (in millions):



	Years ended December 31,
	2017		2016		2015
Revenues:
United States	$	18,029	$	18,326	$	17,167
Rest of the world (ROW)	4,820		4,665		4,495
Total revenues	$	22,849	$	22,991	$	21,662



	December 31,
	2017		2016
Long-lived assets:
United States	$	2,349	$	2,328
Puerto Rico	1,527		1,591
ROW	1,113		1,042
Total long-lived assets	$	4,989	$	4,961

Major customers

In the United States, we sell primarily to pharmaceutical wholesale distributors that we utilize as the principal means of distributing our products to healthcare providers. Outside the United States, we sell principally to healthcare providers and/or pharmaceutical wholesale distributors depending on the distribution practice in each country. We monitor the financial condition of our larger customers and limit our credit exposure by setting credit limits and, in certain circumstances, by requiring letters of credit or obtaining credit insurance.

We had product sales to three customers each accounting for more than 10% of total revenues for each of the years ended December 31, 2017, 2016 and 2015. For the year ended December 31, 2017, on a combined basis, these customers accounted for 81% and 96% of total gross revenues and U.S. gross product sales, respectively, as noted in the following table. Certain information with respect to these customers was as follows (dollar amounts in millions):



	Years ended December 31,
	2017			2016			2015
AmerisourceBergen Corporation:
Gross product sales	$	10,742		$	10,100		$	10,038
% of total gross revenues	31		%	31		%	34		%
% of U.S. gross product sales	37		%	38		%	42		%
McKesson Corporation:
Gross product sales	$	10,625		$	9,710		$	8,766
% of total gross revenues	30		%	30		%	30		%
% of U.S. gross product sales	35		%	34		%	34		%
Cardinal Health, Inc.:
Gross product sales	$	7,049		$	6,520		$	5,045
% of total gross revenues	20		%	20		%	17		%
% of U.S. gross product sales	24		%	24		%	21		%

As of December 31, 2017 and 2016, amounts due from these three customers each exceeded 10% of gross trade receivables and accounted for 75% and 76%, respectively, of net trade receivables on a combined basis. As of December 31, 2017 and 2016, 14% and 21%, respectively, of trade receivables, net, were due from customers located outside the United States, primarily in Europe. Our total allowance for doubtful accounts as of December 31, 2017 and 2016 was not material.