How much yeast does beer have?

I am looking to make some beer bread by substituting beer for water in some of my favorite recipes. I have heard that beer has yeast though, so I was wondering if the yeast in beer would work to ferment & proof my bread.

I was wondering if there is enough for say, an overnight rise without adding any extra yeast, or should I still use the full amount of yeast in each recipe that I use without the beer?