Dijkstra implementation for large graphs
Don't use QT objects when you are not working with QT constructs. There is no benefit to it.
Your node::_id is unsigned shirt, which for MSVS has a range of 0 to 65,535. Be aware of that when you graph grows.
Do not use a map. A std::vector is way faster/bettter for traversing than a std::map. 
You do a lot of copying data around:

QMap&lt;Node*, unsigned short&gt; nextNodes = minNode-&gt;nextNodes();



That is a copy of all neighbors everytime you access a node during your search. If you really need the temporary, which you dont then at least make this a reference.