Revenue

Approximately two-thirds of the Company's net sales are to distributors who then sell directly into the residential, non-residential, industrial, electrical transmission and distribution and oil and gas end markets. Within the Power segment, our businesses sell to distributors, with the majority of sales to the utility end markets. Our businesses within the Power segment also sell directly into transmission and distribution utility markets.

The following table presents disaggregated revenue by business group (in millions) for the twelve months ended December 31, 2018, 2017 and 2016:



	Twelve Months Ended December 31,
	2018		2017		2016
Net sales
Hubbell Commercial and Industrial	$	910.8	$	864.5	$	846.9
Hubbell Construction and Energy	799.7		732.6		667.5
Hubbell Lighting	950.1		935.7		945.8
Hubbell Power Systems	1,821.1		1,136.0		1,045.0
Total net sales	$	4,481.7	$	3,668.8	$	3,505.2

The following table presents disaggregated third-party net sales by geographic location (in millions) for the twelve months ended December 31, 2018, 2017 and 2016 (on a geographic basis, the Company defines "international" as businesses based outside of the United States and its possessions):



	Twelve Months Ended December 31, 2018						Twelve Months Ended December 31, 2017						Twelve Months Ended December 31, 2016
	Electrical		Power		Total		Electrical		Power		Total		Electrical		Power		Total
Net sales
United States	$	2,365.4	$	1,675.2	$	4,040.6	$	2,229.3	$	1,051.6	$	3,280.9	$	2,187.0	$	960.4	$	3,147.4
International	295.2		145.9		441.1		303.5		84.4		387.9		273.2		84.6		357.8
Total net sales	$	2,660.6	$	1,821.1	$	4,481.7	$	2,532.8	$	1,136.0	$	3,668.8	$	2,460.2	$	1,045.0	$	3,505.2

Contract Balances

Our contract liabilities consist of advance payments for products as well as deferred revenue on service obligations and extended warranties. The current portion of deferred revenue is included in Other accrued liabilities and the non-current portion of deferred revenue is included in Other non-current liabilities in the Consolidated Balance Sheet.

Contract liabilities were $27.7 million as of December 31, 2018 compared to $10.2 million as of December 31, 2017. The $17.5 million increase in our contract liabilities balance was primarily due to timing of advance payments on certain orders and the acquisition of Aclara, partially offset by the recognition of $9.0 million in revenue related to amounts that were recorded in contract liabilities at January 1, 2018. The Company has an immaterial amount of contract assets relating to performance obligations satisfied prior to payment that is recorded in Other long-term assets in the Consolidated Balance Sheet. Impairment losses recognized on our receivables and contract assets were immaterial in the twelve months ended December 31, 2018. See Note 1 – Basis of Presentation and Note 3 – Business Acquisitions in the Notes to Consolidated Financial Statements for additional information.

Unsatisfied Performance Obligations

The Company has elected the practical expedient to disclose only the value of unsatisfied performance obligations for contracts with an original expected length greater than one year. Prior to the acquisition of Aclara, the majority of Hubbell's revenues resulted from sales of inventoried products with short periods of manufacture and delivery and thus are excluded from this disclosure. As of December 31, 2018, the Company had approximately $530 million of unsatisfied performance obligations for contracts with an original expected length of greater than one year, primarily relating to long-term contracts of the Aclara business (within the Power segment) to deliver and install meters and grid monitoring sensor technology. The Company expects that a majority of the unsatisfied performance obligations will be completed and recognized over the next 3 years.

Practical Expedients

We apply a practical expedient to expense costs to obtain a contract as incurred when the amortization period would have been one year or less.