I solved the sudden battery drain (the -17% or so per hour while idling) on my Lumia 920 by locking it to only using 3G bands (HSPA/HSPA+) under field test (##3282#, settings, toggle ENS off, network type: 3G only). I'm pretty sure in my case, it has all to do with the LTE (or who knows, maybe it's the 2G? lol) bands. Now I don't know who is to blame (Microsoft, Nokia, Qualcomm, or ATT LTE), but I have not had the random battery drain for the last three weeks that I locked the phone to 3G bands. In comparison, I've had the random battery drain happen almost every other day when I let the phone use LTE. My day to day has not changed in the last three weeks compared to before the three weeks.
Just to try to nail down to it being caused by LTE, I did leave everything turned on in background tasks and kept things on that was purported to cause the massive battery drain during the last three weeks.
On my phone:
Location: On
Tap + Send: On
Background tasks: 6tag, Bing News, Bing Weather, myTube, and Wikipedia: On.
Mail Sync: As Items Arrive.
Has anyone else tried limiting their phone to just 3G bands to see if it stops the random battery drain? Or is my Lumia 920 an anomaly?
P.S. I live in an area that gets full bar of LTE...