Split Cost Allocation Data for ECS tasks can be reported on with FlexReports.
Once the Split Cost Allocation Data options are enabled for the billing account in AWS Cost Management and AWS CUR settings, the SplitLineItem columns will be included in the FlexReports Measures section. The Measures section depicting the SplitLineItem options is pictured below:
The steps to enable Split Cost Allocation data in the AWS Console are located at the link below:
Improve cost visibility of Amazon ECS and AWS Batch with AWS Split Cost Allocation Data