they have about $65 billion in trading assets, although they trade debt securities this week you will notice that they filed with the SEC they recently issued debt backed by stock by Berkshire Hathaway and then again backed by MSCI (not sure) Also some people are not familiar with Wells Fargo as being a market maker.
Since merging with Wachovia they at one point invested a couple hundred million to purchase software for what I call computer trading. Others might call it algorithmic or high frequency trading. What ever it is, they provide a market and deal with "dark and lit pools". I realize this doesn't answer your question, but I am very unsure in what all goes into their trading.
I normally think of their trading income as going up when the market is going up, but I am not sure, please don't base your view on next q line item as being down because the market is down, because its just my intuition.
What you might do is go to their website and do a search on "WATS" which will give you a glimpse of what they do for their customers.