Trouble in fetching firebase data

I need to fetch data from firebase database. I am able to get data of "dueDate" through {{currentBill?.dueDate}} but don't know how to get data of other items above it. Following is the code used to fetch data:

ionViewDidEnter(){
      this.firebaseData.getBillDetail(this.navParams.get('billId'))
      .on('value', snapshot => {
        this.currentBill = snapshot.val();
        this.currentBill.id = snapshot.key;
      });

    }

Kindle help