[sklargh]

Assuming US due to agency choice. What about a 1099-INT? Surely even trivial interest earnings on 10mm would trigger this?

Moreover I'd expect that any given user w/10mm would be rolling into multiple accounts to maximize protection offered by FDIC.

[pjscott]

If you put the money mostly into bonds or stocks that don't issue significant dividends, you'll pretty much just have to worry about capital gains (form 1099-B), and those aren't taxed until the fiscal year in which they're realized.