Press Ctrl + 1 to open the Format Cells window.
Under the tab Number, select Number in the Category list, set Decimal places as 0.
If you want Excel to automatically fully display such long numbers, you can select the area where such numbers could appear, and then apply the number format I mentioned above.
Note that do not apply the number format to the range where includes dates, times or other number formats. If you do, these values will be converted to pure numbers.