17 CFR 22.4: Futures Commission Merchants and derivatives clearing organizations: Permitted Depositories.

In order for a depository to be a Permitted Depository:

(a) The depository must (subject to § 22.9) be one of the following types of entities:

(1) A bank located in the United States;

(2) A trust company located in the United States;

(3) A Collecting Futures Commission Merchant registered with the Commission (but only with respect to a Depositing Futures Commission Merchant providing Cleared Swaps Customer Collateral); or

(4) A derivatives clearing organization registered with the Commission; and

(b) The futures commission merchant or the derivatives clearing organization must hold a written acknowledgment letter from the depository as required by § 22.5 of this part.