By default you can copy detail lines from a project drafting view into a detail component family.  You cannot however copy a detail component from a project drafting view into a detail component family.

There may be a scenario where you have a number of detail lines, and components organized in a drafting view.  What if you want to move this content all into a new detail component family for standard details?

I’ve included 3 options below depending on the complexity of the drafting view or desired detail component:

1.  Edit the detail component family from the project drafting view, and then copy & paste the detail lines [in the family] from the detail component family into the project drafting view.  When complete you could then copy all of the detail items from the project drafting view into a new detail component family.

 
2.  If you are on Subscription, and have access to the Revit Extensions Manager > Freeze Drawings tool, you can create a new drafting view containing a number of detail components.  The resulting "frozen" drafting view will contain an import instance [of the detail component families & lines] which can be partially exploded to detail content or simply copied into a new detail component family.

 
3.  You can copy & paste the detail lines from the project drafting view into a new detail component family.  Then you can load the detail component families into the new detail component family to easily nest and arrange them as needed.