There's a wide variety in terms of the different types of collateral that could be pledged to fulfill your obligation if you are required to pledge some collateral. The collateral that you'll be allowed to deliver, if required to do so, will typically be determined within documentation in place between counterparties. The most standard form of collateral is either cash or G10 government bonds. These are the most desired forms of collateral because they have the least risk associated with them. There's no credit and no market risk attached to cash and limited credit and market risk attached to G10 government bonds. The alternative forms of collateral have more risk attached to them, that being mortgage-backed securities, corporate bonds, letters of credit, and companies equity, stocks and shares. To reinforce the point about cash and government securities being the most desired forms of collateral, this table shows data from the 2015 ISDA Margin Survey, looking at collateral amounts that were pledged during 2014.

There's over $1 trillion worth of collateral making up the data of this table. And in terms of those amounts, we can see that, by far, the largest hub of collateral is cash and government securities, which together make up over 90% of all collateral pledged during 2014. The other forms of collateral previously mentioned, mortgage-backed securities, corporate bonds, letters of credit, and equities were used to some extent during 2015, but to a much smaller extent.