BMO Global Asset Management is selling its retirement business to OneAmerica for an undisclosed sum.

OneAmerica is to acquire BMO's Milwaukee-based US retirement services business, BMO Retirement Services, as BMO said it looks to continue focusing on its asset management business.

Financial details of the agreement were not disclosed but the transaction is expected to close in the third quarter of 2015.

The BMO business will be called OneAmerica Retirement Services, which will continue operating from BMO Retirement Services' current locations. Most clients will continue to work with their current service teams, and BMO Retirement Services employees covered by the agreement will become OneAmerica employees.

"The transaction will not change BMO's role in managing a portion of the investments in the plans moving over to OneAmerica as well as acting as the directed trustee and custodian for those plans," said Barry McInerney, co-chief executive of BMO Global Asset Management.

A year ago, OneAmerica announced an agreement to acquire City National Bank's San Diego, CA-based retirement services business, with 240 plans and $6.5 billion in assets under administration. The BMO deal will further boost its assets under administration by around $26 billion, taking its total to over $70 billion.