When entering this Form 1099-R, TurboTax will ask if the amount in box 2a is the taxable amount. Answer No, select the use of the General Rule, then enter the taxable amount. TurboTax will place this amount in box 2a for you. (Alternatively you could just enter the taxable amount in box 2a yourself and tell TurboTax that box 2a shows the correct taxable amount since this is the result of using the General Rule in TurboTax.)
As extra information you could enter the cost basis (investment in the contract) in box 5, but TurboTax will already assume that the amount that should have been in box 5 is the amount in box 1 minus the amount taxable amount placed in box 2a.
