This article explains the meaning of Idle CPU shown in Junos devices output.

root@juniper> show system processes extensive 
last pid: 7777; load averages: 0.14, 0.03, 0.01 up 1858+09:29:24  03:37:10

144 processes: 4 running, 118 sleeping, 2 zombie, 20 waiting


Mem: 843M Active, 98M Inact, 255M Wired, 2032M Cache, 69M Buf, 39M Free
Swap: 1106M Total, 1106M Free


 PID USERNAME THR PRI NICE  SIZE  RES STATE  TIME  WCPU COMMAND

  10 root    1 171  52   0K  12K RUN    ??? 92.68% idle. >>>>> Idle percent is 92
 7741 ENG     1 96  0 29560K 27564K select  0:01 2.69% cli

The Idle process listed in the JunOS processes, is not actually using CPU resources, but rather represents the percentage of CPU that is currently not being used. In other words, it's a measure of how much of your CPU is idle and available for other tasks.

If you see the idle Process at 50%, that means your CPU is only using 50% of its processing power, and 50% is idle. When the overall CPU usage is 100%, that means the entire CPU is being used. However, the idle Process isn't using any of it. It's just showing you the percentage of CPU that is currently doing nothing. 

There's no risk associated with the Idle Process. It's an essential part of the JunOS operating system that manages the CPU when it's not actively engaged in tasks. If you have high CPU usage from other processes, that's where you should investigate to determine if there are issues that need addressing. To understand what is causing high CPU usage and if there's any risk to your system, look at the other processes in the <show system processes extensive> output.