In the history of U.S. futures trading, the clearinghouse has never defaulted.
Other information on the clearinghouse:
The clearinghouse guarantees that traders in the futures market will honor their obligations. The clearinghouse does this by splitting each trade once it is made and acting as the opposite side of each position. The clearinghouse acts as the buyer to every seller and the seller to every buyer. By doing this, the clearinghouse allows either side of the trade to reverse positions later without having to contact the other side of the initial trade. This allows traders to enter the market knowing that they will be able to reverse their position any time that they want. Traders are also freed from having to worry about the other side of the trade defaulting, since the other side of their trade is now the clearinghouse.
To safeguard the clearinghouse, the exchange requires traders to post margin and settle their accounts on a daily basis.