[wflynny]

See the Involuntary Bumping subsection under Overbooking in [1]. The airline is obligated to give you either:

    `min(2 * your ticket price, $675)`; or 
    `min(4 * your ticket price, $1350)`

depending on how quickly they can reroute you to your destination. You also have legal standing to demand they pay you with a cashier's cheque instead of a voucher.

Judging by personal anecdotes I've read around the web, airlines may be willing to pay more if they are in a bind. But note that this whole voluntary/involuntary bumping procedure happens before you scan your ticket and board the airplane.

[1]: https://www.transportation.gov/airconsumer/fly-rights