Why Is Howard Sending Our $51 Billion Future Fund To The USA?

Please explain:

Chicago-based Northern Trust has been selected by the federal government's Future Fund to provide global custody and related services to the fund, which has $A51 billion (US$42 billion) in assets.

The mandate is the largest custody mandate yet to be awarded by an Australian institution...

Northern Trust Corporation is a provider of investment management, asset and fund administration, fiduciary and banking solutions for corporations, institutions and affluent individuals worldwide.

I'm no economist, but surely this money should be staying in Australia. Surely we have institutions here that are more than capable of providing "custody and related services"? What happens to the fund if and when the US economy implodes? I hope we will be hearing more about this.