I don't claim to be an expert, but I'll have a go:
Again the APRA tables also seem to confirm this situation (Total loans $1,483B, total deposits $1,243B). But if you download the spreadsheet at the link I posted, you will see that "Total Resident Assets" of all banks in Australia is $2,324B, which includes cash and liquid assets held, trading securities, investments (+ all loans) and so on. Ie, if you take the loans out, there are still another $900B of other non loan assets held in the system. So by that measure the banks appear to be well capitalised relative to the size of their loan/deposit books to me?
Just wanted to correct some typo's above - where my original post states $900M I of course meant $900B. Additionally I used decimal points in some of the other numbers where I meant to use comma's! Corrections in the quote above.
In a country with no bank, there is $1 mill of currency. you and a group of entrepreneurs pool your money together and start up a bank with $100k of capital.
Your first customer takes out a loan of $10k with 10% interest per annum.
Total Loans are greater than total deposits by $100,000, unless you count the 100k of capital as deposit.
Excellent example, and I think that's very much the situation with Australian banks, as this shows where the "extra" $900B in resident assets has probably come from (share-holder equity + retained earnings/cash-flow etc).
PS: Thinking about this some more, if we presume an average interest rate margin of say 2% on all outstanding loans, that generates some $30B a year in net cash-flow (ie after paying all funding costs, interest to depositors etc etc), equals 2.5% of the total deposit book pa. We haven't added in cash-flow from bank fee's yet either, which is a similar amount from memory. I would reckon all this cash-flow, plus the non loan related $900B worth of other liquid assets mentioned above, would be more than enough for the banks to cover any deposit withdrawals that might arise under any "normal" circumstances. Does that show how the situation is quite sustainable?
PPS: Looking at all this, it's no wonder the banks have such high earnings and high dividend yields in Australia.
Cheers,
Beej