That should be reported on a Form 1099-R. You enter that in the Wages and Income section of TurboTax, then Retirement Plans and Social Security. Choose the IRA, 401(k), Pension Plan Withdrawals (1099-R) option:
If you don't have a Form 1099-R and can't get one from the pension company, choose the option to enter a substitute Form 1099-R.