Employee Expense Reimbursements/Corporate VISA Cards

I have 2 questions:

1)  For employee expense reimbursements for mileage, what is required for documentation?  Do you allow the employee to put a generic description or is a specific description business purpose allowed.  (meeting with XYZ vs meeting with XYZ and the purpose of the meeting)

2) For corporate VISA cards, are managers required to sign off on expenses incurred by employees that have/use corporate VISA cards? 

Thanks!