Google has multiple ad networks but let's just examine search ads:
Google claims they process 1.2 trillion searches per year. The average clickthrough rate of a google search result ad is around 2%. In demand search results show as many as four ads or more. The average CPC of a Google Adwords click is $1.50.
Let's estimate that 20% of Google search result pages display 4 ads.
1.2 trillion search results * 0.2 results with 4 ads * 0.08 clickthrough rate of at least one ad * $1.5 per click = $28.8 billion.
That gets us part of the way to $110 billion and we haven't even looked at Google shopping ads, Google's display ad network, Youtube ads, or any of their other ad generating properties.
You asked if these are all accidental clicks, but if they were, people would eventually stop paying for them. Businesses pay because they get real business results from them. Yes, most people don't click on ads, but Google's numbers say that about 1 in 50 people do. And that's enough to generate billions in revenue due to Google's search volume.