To give you a bit more explanation in addition to the answer provided by Champ Hal_Al, the amount of the withholdings that you would get back will depend on your tax return as a whole.
All of your income as well as your filing status can affect whether you will get back 100% of the withholding or just a portion of it, or even none at all. For example, if you use the Married Filing Separate filing status, then at least a portion of your Social Security income will likely be taxed and you may even owe additional income tax over and above the amount that was withheld from your 401k distribution.
@Catkt