Trade accounts receivables and unbilled services consist of the following:


(in millions)	March 31, 2026		December 31, 2025
Trade accounts receivable	$	1,632	$	1,668
Unbilled services	1,763		1,783
Trade accounts receivable and unbilled services	3,395		3,451
Allowance for doubtful accounts	(49)		(51)
Trade accounts receivable and unbilled services, net	$	3,346	$	3,400

Unbilled services and unearned income were as follows:


(in millions)	March 31, 2026		December 31, 2025		Change
Unbilled services	$	1,763	$	1,783	$	(20)
Unearned income	(2,261)		(2,118)		(143)
Net balance	$	(498)	$	(335)	$	(163)

Unbilled services, which is comprised of approximately 73% and 71% of unbilled receivables and 27% and 29% of contract assets as of March 31, 2026 and December 31, 2025, decreased by $20 million as compared to December 31, 2025. Contract assets are unbilled services for which invoicing is based on the timing of certain milestones related to service contracts for clinical research whereas unbilled receivables are billable upon the passage of time. Unearned income increased by $143 million over the same period resulting in a decrease of $163 million in the net balance of unbilled services and unearned income between March 31, 2026 and December 31, 2025. The change in the net balance is driven by the difference in timing of revenue recognition in accordance with Accounting Standards Codification ("ASC") 606, Revenue from Contracts with Customers, primarily related to the Company’s Research & Development Solutions contracts (which is based on the percentage of costs incurred) versus the timing of invoicing, which is based on certain milestones.

The Company has accounts receivable factoring agreements to sell certain eligible unsecured trade accounts receivable, either based on automatic arrangements or at its option, without recourse, to unrelated third-party financial institutions for cash. During the three months ended March 31, 2026, through its accounts receivable factoring arrangements that the Company utilizes most frequently, the Company factored approximately $182 million of customer invoices on a non-recourse basis and received approximately $180 million in cash proceeds from the sales. During the three months ended March 31, 2025, through these same accounts receivable factoring arrangements, the Company factored approximately $167 million of customer invoices on a non-recourse basis and received approximately $166 million in cash proceeds from the sales. The fees associated with these transactions were immaterial. The Company has other accounts receivable arrangements for which the activity associated with them is immaterial.