FlexReporting differs from Cost History in that Cost measures are split per LineItemType and everything isn't represented under one "Cost" measure as is the case in Cost History.
You will find in FlexReporting that some Lines for resources return 0 under Net Unblended Cost or Unblended Cost and will display a LineItemType other than "Usage"
For the most part lines with LineItemType Usage will have their cost reflected under Net Unblended Cost or Unblended Cost depending on if the Customer has automated EDP discounting applied by AWS.
If a Customer has EDP automation applied the Net Columns will appear in FlexReporting and should be utilized as these are the columns the "Cost" measure in reporting will reflect currently. If these don't appear please use the non Net fields mentioned below.
For LineItem Type DiscountedUsage this indicates that a Reservation cost savings measure has been applied to the resource represented by the line item. To align with the Cost displayed in the statement drilldown for this resource you would want to make use of Measure -> Reservation -> Net Effective Cost or Effective Cost.
For LineItem Type SavingsPlanCoveredUsage this indicates that a Savings Plan has covered part or all of the usage of the resource mentioned in the Line Item. To align with the Cost displayed in the statement drilldown for this resource you would want to make use of Measure -> Savings Plan -> Net Savings Plan Effective Cost or Savings Plan Effective Cost.