Revenue is recognized when control of promised goods or services is transferred to our customers in an amount that reflects the consideration to which we expect to be entitled in exchange for those goods or services. Substantially all of our revenue is recognized when products are shipped or delivered to our customers, and payment is due from our customers at the time of billing with a majority of our customers having 30-day terms. Returns are estimated and recorded as a reduction of revenue. Amounts received in advance of shipment are deferred and recognized when the performance obligations are satisfied. Sales taxes collected from customers and remitted to governmental authorities are accounted for on a net basis and, therefore, are excluded from sales in the accompanying consolidated statements of operations. Cost of sales includes the cost of inventory sold and related items, such as vendor rebates, inventory allowances and reserves and shipping and handling costs associated with inbound and outbound freight, as well as depreciation and amortization and amortization of intangible assets. In some cases, particularly with third-party pipe shipments, shipping and handling costs are considered separate performance obligations, and as such, the revenue and cost of sales are recorded when the performance obligation is fulfilled.

Our contracts with customers ordinarily involve performance obligations that are one year or less. Therefore, we have applied the optional exemption that permits the omission of information about our unfulfilled performance obligations as of the balance sheet dates.

Contract Balances: Variations in the timing of revenue recognition, invoicing and receipt of payment result in categories of assets and liabilities that include invoiced accounts receivable, uninvoiced accounts receivable, contract assets and deferred revenue (contract liabilities) on the consolidated balance sheets.

Generally, revenue recognition and invoicing occur simultaneously as we transfer control of promised goods or services to our customers. We consider contract assets to be accounts receivable when we have an unconditional right to consideration and only the passage of time is required before payment is due. In certain cases, particularly those involving customer-specific documentation requirements, invoicing is delayed until we are able to meet the documentation requirements. In these cases, we recognize a contract asset separate from accounts receivable until those requirements are met, and we are able to invoice the customer. Our contract asset balance associated with these requirements, as of March 31, 2020 and December 31, 2019, was $21 million and $26 million, respectively. These contract asset balances are included within accounts receivable in the accompanying consolidated balance sheets.

We record contract liabilities, or deferred revenue, when cash payments are received from customers in advance of our performance, including amounts which are refundable. The deferred revenue balance at March 31, 2020 and December 31, 2019 was $5 million and $4 million, respectively. During the three months ended March 31, 2020 and 2019, we recognized $2 million and $5 million of revenue that was deferred as of December 31, 2019 and 2018, respectively. Deferred revenue balances are included within accrued expenses and other current liabilities in the accompanying consolidated balance sheets.

Disaggregated Revenue: Our disaggregated revenue represents our business of selling PVF to the energy sector across each of the upstream production (exploration, production and extraction of underground oil and gas), midstream pipeline (gathering and transmission of oil and gas), gas utilities and downstream and industrial (crude oil refining and petrochemical and chemical processing and general industrials) sectors in each of our reportable segments. Each of our end markets and geographical reportable segments are impacted and influenced by varying factors, including macroeconomic environment, commodity prices, maintenance and capital spending, and exploration and production activity. As such, we believe that this information is important in depicting the nature, amount, timing and uncertainty of our contracts with customers.

The following table presents our revenue disaggregated by revenue source (in millions):


Three Months Ended
March 31,

	U.S.		Canada		International		Total
2020:
Upstream production	$	139	$	37	$	46	$	222
Midstream pipeline		110		4		5		119
Gas utilities		199		3		-		202
Downstream & industrial		190		6		55		251
	$	638	$	50	$	106	$	794
2019:
Upstream production	$	206	$	46	$	60	$	312
Midstream pipeline		133		6		8		147
Gas utilities		204		10		-		214
Downstream & industrial		236		6		55		297
	$	779	$	68	$	123	$	970