Our operations primarily consist of providing collection, transfer and disposal of non-hazardous solid waste, recovering and recycling of certain materials, and energy services. The following table disaggregates our revenue by service line for the years ended December 31 (in millions of dollars and as a percentage of revenue):



	2018					2017					2016
Collection:
Residential	$	2,235.1		22.3	%	$	2,285.7		22.8	%	$	2,239.7		23.9	%
Small-container	3,057.5			30.5		2,995.6			29.8		2,877.5			30.7
Large-container	2,181.1			21.7		2,087.9			20.8		1,975.8			21.0
Other	43.8			0.4		44.2			0.4		38.2			0.4
Total collection ⁽¹⁾	7,517.5			74.9		7,413.4			73.8		7,131.2			76.0
Transfer	1,243.9					1,209.5					1,157.6
Less: intercompany	(706.4		)			(703.8		)			(694.1		)
Transfer, net	537.5			5.4		505.7			5.0		463.5			4.9
Landfill	2,291.7					2,224.3					2,083.6
Less: intercompany	(1,020.8		)			(985.5		)			(962.4		)
Landfill, net	1,270.9			12.7		1,238.8			12.3		1,121.2			11.9
Energy services	194.7			1.9		149.0			1.5		76.4			0.8
Other:
Recycling processing and commodity sales⁽²⁾	298.0			3.0		539.2			5.4		420.4			4.5
Other non-core	222.3			2.1		195.4			2.0		175.0			1.9
Total other	520.3			5.1		734.6			7.4		595.4			6.4
Total revenue	$	10,040.9		100.0	%	$	10,041.5		100.0	%	$	9,387.7		100.0	%

(1) In accordance with our adoption of the new revenue recognition standard, municipal franchise fees were presented as a reduction to revenue for the year ended December 31, 2018. Similar fees were presented as a cost of operations for the years ended December 31, 2017 and 2016.

(2) In accordance with our adoption of the new revenue recognition standard, rebates paid to customers associated with recycled commodities were presented as a reduction to revenue for the year ended December 31, 2018. Similar costs were presented as a cost of operations for the years ended December 31, 2017 and 2016.

Other non-core revenue consists primarily of revenue from National Accounts, which represents the portion of revenue generated from nationwide or regional contracts in markets outside our operating areas where the associated waste handling services are subcontracted to local operators. Consequently, substantially all of this revenue is offset with related subcontract costs, which are recorded in cost of operations.

The factors that impact the timing and amount of revenue recognized for each service line may vary based on the nature of the service performed. Generally, we recognize revenue at the time we perform a service. In the event that we bill for services in advance of performance, we recognize deferred revenue for the amount billed and subsequently recognize revenue at the time the service is provided. Depending upon the nature of the contract, we may also generate revenue through the collection of fuel recovery fees and environmental fees which are designed to recover our internal costs of providing services to our customers.

Our collection business involves the collection of waste for transport to transfer stations, or directly to landfills or recycling processing centers. Our solid waste collection services business includes both recurring and temporary customer relationships. Our standard contract duration is three years, although some of our exclusive franchises are for significantly longer periods. The fees received for collection services are based primarily on the market, collection frequency, type of service, type and volume or weight of the waste collected, the distance to the disposal facility and the cost of disposal.

In general, small-container and residential collection fees are billed monthly or quarterly in advance. Substantially all of the deferred revenue recognized as of December 31, 2017 was recognized as revenue during the year ended December 31, 2018 when the service was performed. Our large-container customers are typically billed on a monthly basis based on the nature of the services provided during the period.

Revenue recognized under these agreements is variable in nature based on the number of residential homes or businesses serviced during the period, the frequency of collection and the volume of waste collected. In addition, certain of our contracts have annual price escalation clauses that are tied to changes in an underlying base index such as a consumer price index which are unknown at contract inception.

Revenue at our transfer stations is primarily generated by charging tipping or disposal fees. The fees received for transfer services are based primarily on the market, type and volume or weight of the waste accepted, the distance to the disposal facility and the cost of disposal. In general, fees are billed and revenue is recognized at the time the service is performed. Revenue recognized under these agreements is variable in nature based on the volume of waste accepted at the transfer station.

Revenue at our landfills is primarily generated by charging tipping fees to third parties based on the volume disposed and the nature of the waste. In general, fees are variable in nature and revenue is recognized at the time the waste is disposed at the facility.

Energy Services revenue is primarily generated through waste managed from vertical and horizontal drilling, hydraulic fracturing, production and clean-up activity, as well as other services including closed loop collection systems and the sale of recovered products. Energy services activity varies across market areas that are tied to the natural resource basins in which the drilling activity occurs and reflects the regulatory environment, pricing and disposal alternatives available in any given market. Revenue recognized under these agreements is variable in nature based on the volume of waste accepted or processed during the period.

Our recycling processing centers generate revenue through the processing and sale of old corrugated cardboard (OCC), old newsprint (ONP), aluminum, glass and other materials at market prices. In certain instances, we issue recycling rebates to our municipal or large-container customers, which can be based on the price we receive upon the final sale of recycled commodities, a fixed contractual rate or other measures. We also receive rebates when we dispose of recycled commodities at third-party facilities. The fees received are based primarily on the market, type and volume or weight of the materials sold. In general, fees are billed and revenue is recognized at the time title is transferred. Revenue recognized under these agreements is variable in nature based on the volume and type of materials sold. In addition, the amount of revenue recognized is based on commodity prices at the time of sale, which are unknown at contract inception.

Our service obligations of a long-term nature, e.g., solid waste collection service contracts, are satisfied over time, and we recognize revenue based on the value provided to the customer during the period. The amount billed to the customer is based on variable elements such as the number of residential homes or businesses for which collection services are provided, the volume of waste collected, transported and disposed, and the nature of the waste accepted. We do not disclose the value of unsatisfied performance obligations for these contracts as our right to consideration corresponds directly to the value provided to the customer for services completed to date and all future variable consideration is allocated to wholly unsatisfied performance obligations.

Additionally, certain elements of our long-term customer contracts are unknown upon entering into the contract, including the amount that will be billed in accordance with annual price escalation clauses, our fuel recovery fee program and commodity prices. The amount to be billed is often tied to changes in an underlying base index such as a consumer price index or a fuel or commodity index, and revenue can be recognized once the index is established for the period.