These benefits would not be taxable if you paid the premiums yourself and didn't take a deduction for them. If your employer paid the premiums or if you paid the premiums with before tax income, you would pay tax on the benefits, and you would receive a W-2 for the taxable amount.
See this link to AFLAC's Frequently Asked Questions:
http://www.aflacgroupinsurance.com/customer_service/faq.aspx
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