Let's facebook!

U.S. Senate published a document with Facebook answers to congressmen's questions, which they asked Mark Zuckerberg, but he did not know the answers and promised to send them in writing. If you have a lot of free time, 225 pages of document are waiting for you:

https://www.commerce.senate.gov/public/_cache/files/ed0185fb-615a-4fd5-818b-5ce050825a9b/62027BC70720678CBC934C93214B0871.senate-judiciary-combined-7-.pdf

And there is an interesting list of information that Facebook collects about users (question 76 and places in the text. Not all of this is obvious to users (e.g. battery level, available disk space, shopping on other sites, etc):

information from "computers, phones, connected TVs, and other web-connected devices," as well as your "internet service provider or mobile operator"
"mouse movements" on your computer
"app and file names" (and the types of files) on your devices
whether the browser window with Facebook open is "foregrounded or backgrounded," and time, frequency, and duration of activities
information about "nearby Wi-Fi access points, beacons, and cell towers" and "signal strength" to triangulate your location ("Connection information like your IP address or Wi-Fi connection and specific location information like your device's GPS signal help us understand where you are," said a Facebook spokesperson.)
information "about other devices that are nearby or on their network"
"battery level"
"available storage space"
installed "plugins"
"connection speed"
"purchases [users] make" on off-Facebook websites
contact information "such as an address book" and, for Android users, "call log or SMS log history" if synced, for finding "people they may know" (Here's how to turn off contact uploading or delete contacts you've uploaded.)
information "about how users use features like our camera" (The Facebook spokesperson explained, "In order to provide features like camera effects, we receive what you see through camera, send to our server, and generate a mask/filter.")
"location of a photo or the date a file was created" through the file's metadata
information through your device's settings, such as "GPS location, camera, or photos"
information about your "online and offline actions" and purchases from third-party data providers
"device IDs, and other identifiers, such as from games, apps or accounts users use"
"when others share or comment on a photo of them, send a message to them, or upload, sync or import their contact information"