183  Note 38.1  Credit risk  continued  parties during the term of arrangements, to mitigate  counterparty risk arising from changes in market values of  the derivatives.  Derivative financial instruments  As at 31 March 2014, Macquarie held OTC contracts with a  positive replacement value of $10,153 million (2013: $9,819  million). The credit risk of these contracts is reduced due to  master netting agreements covering negative OTC contracts  of $6,235 million (2013: $6,170 million) and margins held  (excluding the impact of over-collateralisation) of  $1,167 million (2013: $687 million). In addition, Macquarie  has placed collateral of $1,643 million (2013: $2,043 million)  which has negligible credit risk as this is fully offset by the  related negative OTC contracts.  Exchange traded derivatives contracts have limited credit risk  as counterparties have to be members of the exchange and  demonstrate they have adequate resources to fulfill  obligations when they become due. Members are required to  provide initial margins in accordance with the exchange rules  in the form of cash or securities, and provide daily variation  margins in cash to cover changes in market values. Further,  all members are generally required to contribute to (and  guarantee) the compensation or reserve fund which may be  used in the event of default and shortfall of a member.  Macquarie has exchange traded derivatives with positive  replacement values (and for which counterparties would  have had to place margin) as at 31 March 2014 of  $2,565 million (2013: $2,610 million). Macquarie has also  placed margins on House and Client positions with  exchanges, the balance at 31 March 2014 being $2,831  million (2013: $3,459 million), which are recorded in  Receivables from financial institutions and Loan assets held  at amortised cost.  Debt investments securities available for sale  Included in this balance are holdings of $nil (2013: $683  million) issued by Australian banks which are subject to an  Australian Government Guarantee. A further $255 million  (2013: $243 million) is secured by specified Australian and  Canadian assets under covered bonds.  Other assets  For Over The Counter (OTC) derivative contracts, Macquarie  often has master netting agreements (usually ISDA Master  Agreements) with certain counterparties to manage the  credit risk. The credit risk associated with positive  replacement value contracts is reduced by master netting  arrangements that in an event of default requires balances  with a particular counterparty covered by the agreement  (e.g. derivatives and cash margins) to be terminated and  settled on a net basis. Macquarie also often executes a  Credit Support Annex in conjunction with a master netting  agreement, which facilitates the transfer of margin between  Security settlements of $6,094 million (2013: $5,567 million)  are included in Other assets, which represent amounts owed  by an exchange (or a client) for equities sold (or bought on  behalf of a client). Macquarie holds the underlying equity  security or cash until settled, which is usually less than 3  days after trade.  Credit commitments and contingent liabilities  Of the Undrawn facilities and lending commitments of  $4,792 million (2013: $3,748 million), $2,129 million (2013:  $1,591 million) are fully secured by underlying specific  assets.