Based on information in your question, this answer is
assuming that you are an employee
receiving a W-2 (not self-employed receiving a Form 1099-MISC).
You mentioned that you are reimbursed at the rate
of $0.14 per mile. Since that reimbursement
per mile is less than the business mileage rate published by the IRS for the
year ($0.54 per business mile for 2016), then you can deduct the difference in those rates. This allows you to take full advantage of the
published standard mileage rate.
As an employee, you would use Form 2106 Unreimbursed Employee Expenses to claim this difference. One important thing to know about Form 2106
is that you must also be using Schedule
A and claiming itemized deductions (not the standard deduction) before it
may affect the bottom line of your tax return.
This means that you could enter all the necessary information into your
return to claim the mileage and your reimbursement amount, but if you are using
the standard deduction then your refund/balance due would not change.
To go to the section of TurboTax to enter any unreimbursed
employee expenses, use these steps:
On the top row of the
TurboTax online screen, click on Search (or for CD/downloaded TurboTax
locate the search box in the upper right corner)
This opens a box where you
can type in “2106” (be sure to enter exactly as shown here) and click
the magnifying glass (or for CD/downloaded TurboTax, click Find)
The search results will
give you an option to “Jump to 2106”
Click on the blue “Jump
to 2106” link
[edit 01/23/17 8:04 am PST - typo]
