Amazon Web Services has 2 cost type: Actual and Estimated.
Estimated costs are a CloudWatch metric. This metric shows the estimated charges for your AWS usage. This can either be estimated charges for one service or a roll-up of estimated charges for all services.
Actual costs are costs from detailed billing report. AWS recreates the detailed billing report multiple times a day, overwriting the report. These costs are your true costs, and may be somewhat delayed.