No, it will not be totally nontaxable. With a year-end balance in your traditional IRAs of $7,000 and a distribution during the year of $13,000, the nontaxable amount of the distribution will be ($13,000 / $20,000) * $13,000 = $8,450 and that taxable amount will be $4,550. $4,550 of your basis in nondeductible traditional IRA contributions will remain in your traditional IRAs to be applied to future distributions.
