a little history...
After the 1929 stock market crash which led into the Great Depression, the Glass-Steagall Act (1933) was passed in order to avoid another financial crash. In part, by reducing commercial speculation by the banks, it hoped to limit the amount of risk that a bank could accept.
Fast forward to 1999, the Gramm-Leach-Bliley basically overturned Glass-Steagall.
Now you may note this was during Clinton's term, but the original passage in the Senate was strictly on a Republican Party line vote (54-44).
However, once the bill went into committee to resolve the House and Senate differences it was approved overwhelmingly (90-8).
As for what this means to our current candidates:
McCain voted for the original bill, and against the committe report.
Biden voted against the original bill, and for the compromise version.
One of the sponsors of the bill was Phil Gramm, now McCain's top economic advisor.
Make of it what you will.