Some pensions contain both an employer and employee contribution (basis).
The employee contribution portion of any distribution would be non-taxable.
Is there an amount in Box 5 of your 1099-R, or another notation, that may indicate to TurboTax that you have a basis in your pension?
If you can clarify, we'll try to help.
Here's more info from the IRS on Pensions and Annuities.