Management wants a report of AWS billed items listed by user for department budget planning. What is the most efficient way to obtain this report?

AWS Cost Explorer is specifically designed for visualizing, understanding, and managing AWS costs and usage over time. It allows you to create custom reports, filter by various dimensions like user, service, and tag, and then download the data, which directly addresses the requirement for a report of billed items by user for budget planning. Running a query with Amazon Athena would require setting up a data source (like Cost and Usage Reports in S3) and writing SQL queries, which is less efficient for a standard reporting need than Cost Explorer's built-in capabilities. Accessing bill details from the billing dashboard provides a high-level overview but lacks the granular filtering and reporting features of Cost Explorer. Modifying a cost budget in AWS Budgets is for setting alerts and tracking against thresholds, not for generating detailed historical reports of billed items by user.