How does the session timeout work in IIS 7?

In web.config, I set timeout in the sessionState to 20 minutes. According to MSDN, this timeout specifies the number of minutes a session can be idle before it is abandoned. In IIS 7, DefaultWebSite->Session State->Cookie Settings->Time Out automatically is populated with timeout value set in web.config, which in my case is 20 minutes. Also, Application Pools->DefaultAppPool->Advanced Settings->idleTimeout, I set it to 10 minutes.