The abbreviations Dr and Cr are not familiar to most Americans outside of accounting circles. Please provide the option to print running customer account balances on statements as numbers in parentheses for credits, or just as numbers if debits. If the bottom-line balance is negative, the words CREDIT BALANCE should appear somewhere, or a configurable memo line should appear that can say something to the order of “Your account has a credit balance. Do not pay.”
Alternatively, I think most Americans would understand the letters CR (both capitals) next to the credit balances. Not DR or Dr, though.