Note that you can't distribute just the after-tax basis from the 401(k) account, the distribution must be a proportionate mix of after-tax basis, and pre-tax money, so if the after-tax basis was directly rolled to the Roth IRA while the pre-tax money was directly rolled to a traditional IRA, the code G Form 1099-R will generally report the sum of the two. To be able to report this split rollover in TurboTax you'll need to split this code G Form 1099-R into two, one for the portion rolled over to the Roth IRA and the other for the portion rolled over to the traditional IRA.
