Baby boomers control an estimated $10 trillion in assets, and financial managers are preparing for a big shift in investment priorities as this age group hits retirement.

Boomers will soon move from accumulation to "decumulation," said one executive at asset manager BlackRock, according to Reuters.

Instead of building a nest egg, the focus will turn to how to make that nest egg last.

This is all very normal, of course, but what's got financial managers worried is how their business will change as this large demographic heads to retirement. Where will this $10 trillion go?

BlackRock has found that retirement-age clients are perfectly happy to move their money to firms with more expertise in managing retirees' money. This area is more complex than normal asset accumulation, said the executive, Frank Porcelli.

"This is the equivalent of financial brain surgery," he said.

So now, don't be surprised to see many firms suddenly become experts in post-retirement money management in an effort to hold on to their clients.