Document presents this as an example, but it will probably correspond to the method the brokers use. Look for PDF titled Tax Basis Information for FNFV Tracking Stock Distribution. They used the closing prices for the first day of trading for their example numbers.
Looking at their example method, they are using June 30 closing prices when the FNF reflected the combination and when FNFV.WI represented just the FNFV part. Using those closing numbers, I come up with 15.37% basis to FNFV. Anybody up for checking the math to see if you can see how they might have come up with 15.11% ? It could be me mis-using a spreadsheet.