From MongoDB into ElasticSearch: Converting meta field of _id

I'm using pymongo to insert a document from MongoDB into Elasticsearch, and getting an error below. The problem looks like the '_id'. How can I convert the "_id" to "id" before inserting it into ElasticSearch?

Error:

elasticsearch.exceptions.RequestError: TransportError(400, 
u'mapper_parsing_exception', u'Field [_id] is a metadata field and 
cannot be added inside a document. Use the index API request 
parameters.')

Code:

for doc in documents1.find():
   doc_sanitized = json.loads(json_util.dumps(doc))
   es.index(index='index-name', doc_type='intel', id=i, body=doc_sanitized)