Because the excess being distributed has already been taxed, it does not need to be reported on your tax return as income. You'll probably receive a code BP 2016 Form 1099-R for this amount with a taxable amount of zero. If you enter this form into TurboTax, it will have no effect on your tax return at all since the taxable amount will be zero. If there are also gains on your excess Roth 401(k) deferral that must be distributed as well, these will be reported on a code 8B 2016 Form 1099-R and will be taxable on your 2016 tax return.
