To accommodate TurboTax's limitations on being able to handle this distribution being split to the two different accounts, you must split the original Form 1099-R into two for entry into TurboTax.
It's a bit unusual that the earnings attributable to the after-tax contributions were rolled over to the Roth IRA, indicated by the nonzero taxable amount inbox 2a, but it is what it is. That cannot be undone. For the portion rolled over to the Roth IRA, the 1099-R form for that portion will have in box 1 the sum of the box 2a and box 5 amounts, the box 2a amount in box 2a and the box 5 amount in box 5. The 1099-R form for the portion rolled over to the traditional IRA will have in box 1 the amount from box 1 of the original form minus the amounts from boxes 2a and 5, and zeros in boxes 2a and 5.
This splitting of the original form will be transparent to the IRS because with no tax withholding, the details of these 1099-R forms entered into TurboTax will not be included in your e-filing. Only the result on Form 1040 lines 5a and 5b will be present in your tax return. Line 5a will include the entire gross amount and line 5b will include only the taxable amount from box 2a. TurboTax will also include the ROLLOVER notation next to the line.
