State Street Corp. has agreed to buy General Electric Co’s asset management unit for up to $485 million as the Boston-based firm works to add scale to its money management division.

The business, which includes GE's US benefits plans as well as assets for third-party institutional client, manages more than $100 billion in assets. The cash deal will give State Street Global Advisors, known for its index-tracking funds, a broader mix of money management abilities including private equity and real estate investments.