By default in Revit you cannot measure the total length of multiple detail lines.
However you can measure the total length of multiple model lines using the Measure Along An Element tool and TAB selecting the chain.
So if you needed a quick total length you could select the detail lines > Convert Lines > Measure Along An Element > TAB > click chain. The Options Bar will list the Total Length, as well as a temporary dimension for each line segment. As needed the model lines could be converted back to detail lines when complete.
Quick video embedded below [no sound]: