Your idea is great. So great even, that there is already a precedence for this sort of thing.

Mint.com, indinero, less accounting, all of them use backend bank services like Yodlee to sync with bank accounts and statements, auto-categorize expenses, and generate visual reports and integrated tracking tools to make accounting and bookkeeping simple.

The question isn't "is my idea good?" it really is "do I have enough of a unique angle to compete with others in that space?"