But a systemically important bank may not be allowed to fail in future, says S&P.
The Reserve Bank's Open Bank Resolution policy might make it difficult for the authorities to defend intervening to bail out a distressed bank, credit-ratings agency Standard and Poor's says.
The agency, in a report on the New Zealand banking sector, said bank ratings would not be negatively affected by progression of an Open Bank Resolution (OBR) policy.
"Resolution regimes, such as New Zealand's OBR policy, are generally established by governments to lessen the damage to the economy and the cost for the taxpayer of a distressed, systemically important, bank," S&P analyst Peter Sikora said in the report.
The OBR policy requires all banks with retail funding of more than $1 billion to "pre-position" their systems so customers would have access to accounts the day after an insolvency event.