<?php
$a = json_decode('{"id":"10000000000000000"}');
$b = json_decode('{"id":"10000000000000001"}');

$ida = $a->id;
$idb = $b->id;

var_dump($a);
var_dump($b);

if (strcmp($ida, $idb)==0) {
  echo 'a==b';
}

object(stdClass)#1 (1) {
  ["id"]=>
  string(17) "10000000000000000"
}
object(stdClass)#2 (1) {
  ["id"]=>
  string(17) "10000000000000001"
}