Table:
|  | December 31, |  |
| --- | --- | --- |
|  | 2019 | 2018 |
| Trade receivables — billed | $136.6 | $136.6 |
| Trade receivables — unbilled | 39.8 | 37.0 |
| Trade receivables | 176.4 | 173.6 |
| Allowance for doubtful accounts | (1.3) | (1.3) |
| Trade receivables, net | $175.1 | $172.3 |
Paragraphs:
Trade Receivables, Net
The carrying amounts reported in the Consolidated Balance Sheets for Trade receivables, net approximate their fair value because of their short-term nature.
A summary of Trade receivables, net of allowance for doubtful accounts is as follows (in millions):
In addition to the amounts above, we have unbilled receivables that we do not expect to collect within the next year included in Other non-current assets in our Consolidated Balance Sheets. Billings for these receivables are based on contractual terms. Refer to Note 11 — Other Non-Current Assets.
Question:
What was the change in trade receivables between 2018 and 2019?