J.P. Morgan & Co. said this week it has completed its  purchase of a 45% stake in American Century Cos., the nation's 20th-largest   mutual fund company.   
The transaction, valued at about $900 million and unveiled in July,  teams a leading global financial institution with a highly regarded   provider of no-load mutual funds.   
  
Morgan manages $240 billion in retirement plans, mutual funds, and  accounts for high-net-worth customers. American Century, based in Kansas   City, Mo., has $62 billion of assets under management.   
The companies said Wednesday that they will initially focus on marketing  defined-contribution retirement plan services to corporations. They will   also pitch their investment offerings to one another's customers and will   jointly pursue mutual fund sales to financial intermediaries and   institutional investors.       
  
"Our business partnership with American Century will accelerate the  growth of our asset management business by adding service and product   expertise, distribution, and technology capabilities," said Jeff Garrity, a   managing director with J.P. Morgan.