pre_text: Contract Assets and Liabilities Contract assets represent the Company’s rights to consideration in exchange for services transferred to a customer that have not been billed as of the reporting date. While the Company’s rights to consideration are generally unconditional at the time its performance obligations are satisfied, under certain circumstances the related billing occurs in arrears, generally within one month of the services being rendered. At the inception of a contract, the Company generally expects the period between when it transfers its services to its customers and when the customer pays for such services will be one year or less. Contract liabilities relate to advance consideration received or the right to consideration that is unconditional from customers for which revenue is recognized when the performance obligation is satisfied and control transferred to the customer. The table below sets forth the Company’s contract assets and contract liabilities from contracts with customers. The increase in the contract assets balance during the period was primarily due to $203 million of revenue recognized that was not billed, in accordance with the terms of the contracts, as of December 31, 2019, offset by $193 million of contract assets included in the December 31, 2018 balance that were invoiced to Nielsen’s clients and therefore transferred to trade receivables. The decrease in the contract liability balance during the period was primarily due to $326 million of advance consideration received or the right to consideration that is unconditional from customers for which revenue was not recognized during the period, offset by $337 million of revenue recognized during the period that had been included in the December 31, 2018 contract liability balance.
table: (IN MILLIONS) Year Ended December 31,
table: 2019 2018
table: Contract assets $218 $210
table: Contract liabilities $346 $359
question: Analyse this data from a financial earnings document. What is the change in the contract assets from 2018 to 2019?