Is the account in Guns, Germs, and Steel given in broad outline or in detail?
The account in this book is at times quite detailed and at times quite broad. Therefore, the best answer to this question is that it is both.
When Diamond is presenting scientific evidence, he is at his most detailed. He gives, for example, charts of the exact numbers of the grasses with large seeds in each part of the world (this is in Table 8.1). This is the sort of evidence which Diamond presents in the most detail.
When it comes to historical evidence and arguments, Diamond paints much broader outlines. He devotes only a few pages to discussing the ways in which China came to dominate all of East Asia. This type of evidence, which would be much more difficult to give in detail, is presented in much broader outlines.