What should we expect flying through Paris (CDG) from Florence?

In Florence, you'll go through airport security like you would in the US (more or less). Probably won't need to take your shoes off.

In Paris, you'll go through passport control as you exit the Schengen zone, then probably through security again (may depend on the airport). Your biggest line is probably going to be through passport control. Last year, when I flew Delta home to the US out of Paris, I had to take a little "airport train" inside the airport to my gate, not very long. I assume you'll have to do the same thing.

You'll go through customs in Detroit after you get through immigration - re-entry to the United States. Unless you have something to declare, customs is a 10 second walk without stopping as you exit baggage claim in Detroit.

You can expect at least as much "security theater" leaving Paris as you would with TSA before a domestic flight. My two most intrusive airport security experiences have been boarding US-bound flights from Europe. And being in Pre-check doesn't help because you're not dealing with TSA.

Years ago, I remember a very casual security process at CDG, then being glared at by two military-looking guys with machine guns at the aircraft door. Very theatrical. More recently they've sharpened up the process.

Expect that at least one of you will get a boarding pass that shows SSSS at CDG on your Delta boarding pass. The SSSS = Secondary Security Screening Selection and you and your baggage will be screened further for explosives. Not a big issue as your hands, luggage and electronics will be wiped down to checked for explosives. This happens on all US bound flights originating in Europe and the Middle East. Haven't seen it on flights originating in Japan and Singapore, but I am sure it is happening. It is mandated by Homeland Security and the TSA and selection is random. Global Entry and TSA Pre-Check does not get you any clearance on this one. Just go with the flow, it does not take too much time.

Is this a single booking?

We flew into CDG from Zurich in May. Air France and Delta are code share partners and share terminal 2 at CDG. So you won't have to change terminals. If I remember correctly, we arrived in Terminal 2 F and departed on a Delta flight from Hall K in Terminal 2. Departures are either from Hall K or Hall L or Hall M. You only need a shuttle to Hall M. The other 2 halls are walkable. We landed around 9 am on a Sat. and had a wait to go through immigration control, but it was not too long. They only checked our passports and then we headed to Hall K for our flight out. What we didn't expect was to land at CDG in some remote open area, descend the plane on metal stairs (open air like you see in old movies) and board a bus to take us to Terminal 2 F! To board our Delta flight was the same in reverse! No Skywalks at all! This was our second and last time going through CGD! I will avoid it like the plague in the future.

Joe32f,
There are 2 of us flying.
This will be on our return trip from Italy.
We are starting our trip home flying from Florence to CDG on Air France connecting to a Delta flight back to Detroit, then back to Cedar Rapids Iowa. I’m probably not understanding your question, but it was all booked through Delta at the same time.
Thanks!

but it was all booked through Delta at the same time.

Good.

My 'single booking" question was to discern if you had done what you did or had purchased the Florence-Paris flight and Paris-DTW as separate transactions. The latter would be susceptible to a host of problems should the 1st flight be delayed.