Google plays the yield curve

Greg Mankiw talks about Google's recent sale of $3billion of bonds.  The sale is a little surprising given that Google is sitting on $37 billion of cash.  One potential explanation is that Google is looking to stock pile more cash in case it wants to go on a spending spree.  An alternative explanation is that Google is seeking to establish a debt rating for future debt issues.  

The details of the deal are documented in the Wall Street Journal article.  Clearly Google has extremely low borrowing costs.

The (Google's) 10-year bond, for instance, will yield 3.734%, compared to 10-year Treasurys, which yield 3.15%.