The combined holdings of residential MBS by banks and thrifts topped the $1.5 trillion mark for the first time ever during the third quarter, as depository institutions without a lot of great alternative investment options continued to plow money into the market. Banks and thrifts held a record $1.533 trillion in residential MBS at the end of September, up 2.8 percent from the previous quarter and 10.4 percent ahead of the same period in 2010. Banks and thrifts held a combined 23.2 percent share of the outstanding residential MBS in the market. The biggest...(Includes two data charts)