Hi there - I don't suppose you ever got anywhere with this issue? I have the exact same problem (see image - note a reboot occurred where the slight gap is):
View attachment 135031
The idle battery drain can be great (say 3% over night) while other times it's horrible. I cannot pin it down to a particular thing though "WiFi" seems to feature higher up the battery usage stats than I would expect...
It seems even if I kill every open app, disable WiFi, disable location services etc. the only "fix" is a reboot. It's a little random but if I leave the phone on without a reboot for a week or so I'll generally get it.
Same exact problem.
Unfortunately, I haven't been able to find a proper culprit and/or solution. It's just something a Nexus owner has to live with. Sometimes, it'll be fine for 2-3 weeks, then the problem will occur. Other times, as little as a week and I'll see the issue. Again, all typical day-to-day usage -- no real outstanding or obvious culprit.
Just a weird, weird bug with either Android or the Nexus 5 device. It's livable, but I'm looking to move to something else if the right device comes along or if Android L somehow magically gets rid of this bug.
Sorry to hear you have the same issue.