From the content editor, is it possible to copy the presentation details, renderings, layout, etc.. from Item A and paste onto Item B?
I'd like to avoid creating a duplicate of A and then resetting the content field values manually.
Yes, the presentation values of Item A are stored as an XML construct in the raw values of the Renderings field.
If you follow the blue arrows and click on Raw Values you'll see:
Raw Values Method
Select the rendering field value, copy, and then in Item B, do the same thing, but PASTE the field value there.
Turn off Raw Values, and you should see the presentation on both Items now.
Editor Method
You can also use the Copy To dialogue as well. Which has been there forever, and I always forget about it.
SPECIAL NOTE
While this is the direct answer to your question, there is an architectural viewpoint that must be considered. Generally, adjusting presentation on Items directly is frown upon, because you break the association that it might have with the Template Standard Values that the Item derives from.
In those cases, generally you only muck with Final Renderings on the item itself, and Renderings on the Template Standard Values that the Item is made from.
For more information on that, take a peek at Sitecore's documentation on editing the layout of an item.
Yes. Open the presentation details of the item you want to copy from. you will see a link "Copy To" beside "Edit". You can pick which target devices you want and to which item you want to copy the presentation details
If you have Sitecore Powershell Extensions installed then there is an OOTB module available to copy/paste renderings between items.
Simply right click the item, then select Scripts > Layout > Copy Renderings
and then select the Paste Rendering
option on the item you want to copy to.