I remember a few years ago the saving interests in Australia was around 8% plus. That was risk-free rate, if you take a bit more risk on other financial products, 10% might be achievable. Not feasible for 20 years though.
I don't know the history of Australian interest rates but the only time US interest rates were at that level was during the inflationary times of the 70's.
This link says current interest rates are 3.5%. [1]
