From the Microsoft Q2 2017 10K filing:
As of June 30, 2017, collateral received under agreements for loaned securities was $3.7 billion, which was primarily comprised of U.S. government and agency securities. As of June 30, 2016, collateral received under agreements for loaned securities was $294 million, which was primarily comprised of cash.
We lend certain fixed-income and equity securities to increase investment returns. The loaned securities continue to be carried as investments on our consolidated balance sheets. Cash and/or security interests are received as collateral for the loaned securities with the amount determined based upon the underlying security lent and the creditworthiness of the borrower. Cash collateral received is recorded as an asset with a corresponding liability. Our securities lending payable balance was $97 million as of June 30, 2017. Our average and maximum securities lending payable balances for fiscal year 2017 were $484 million and $1.5 billion, respectively. Intra-year variances in the amount of securities loaned are mainly due to fluctuations in the demand for the securities.