Because this is a reverse auction, the 10 billion would become (in the event that the round's forward auction was a success) a debt that the FCC would owe the TV stations for their channels that they are giving up. Until a successful round (where the forward auction bid total* is considerably greater than the reverse auction total), there's no "it" to hold. I'm sure the FCC would be willing to consider the transfer of any existing debt to you.
* a dollar figure that must cover:
- the reverse auction debt
- the combined cost of conducting all of the auction rounds
- subsidies to non-auction-participating stations for the cost of moving to different frequencies
- funding for ongoing FCC operations
- viggerish