"[H]ealth insurers and third party administrators are often required to pay the tax, and it is expected that these third parties will generally demand reimbursement from employers. Reimbursements for the non-deductible Cadillac tax would have constituted taxable income to the health insurers. Insurers had already indicated that they expected employers to reimburse them for these additional taxes on the Cadillac tax reimbursements, ultimately costing employers 50 to 60 percent, rather than 40 percent, of the value of excess benefits provided. Now that the Cadillac tax is deductible, the tax's burden on employers should actually approximate the size of the tax."