failed to access to a value in a json variable

I have some troubles with a variable after doing some mongodb processing

...................
console.log("MIP : value :" + value._id );
console.log("MIP : page id :" + value._id.id ); 
....................

The logs show this

MIP : value :{ id: '346593403645', _id: 57a868497e07fcf75f27009c, __v: 0 }
MIP : **page id :undefined**

I am not understanding why the value of value._id.id is undefined

Could you help please