As with any distribution from a qualified retirement plan, the plan will issue a Form 1099-R that must be included on your tax return (by entering it into TurboTax) so that the actual tax liability resulting fro the distribution can be determined.
Tax withholding is nothing more than a down-payment toward the overall tax liability determined on your tax return. Tax withholding does not apply to any particular item of income on your tax return even though the amount might have been be calculated based on a particular item of income. In the case of an RMD, which is not eligible for rollover, the tax withholding can generally be any amount you desire and will be credited on your tax return.
