In January you will receive a 1099R, which you must enter on your 2017 tax return to report the retirement fund distribution. The 20% that was withheld was an estimate of tax you may owe. If you withdrew the money before you were 59 1/2 there will also be an early withdrawal penalty of 10%.
On your 2017 return-To enter your retirement income, Go to Federal> Wages and Income>Retirement Plans and Social Security>IRA 401 k) Pension Plan Withdrawals to enter your 1099R.