S&P cuts Australia's 'big four' banks' credit outlook to negative

Credit outlook for CBA, Westpac, ANZ, and NAB were all cut

• Ratings/Outlook were cut from AA-/Stable to AA-/Negative

The reasoning for downgrade by S&P is that it reflects the country's sovereign credit outlook downgrade earlier, which means a "slightly reduced financial capacity to provide timely financial support to the systemically important financial institutions, if needed".

Just take note that Fitch had yesterday downgrade its rating for Australia's 'big four' banks due to coronavirus risks as seen here.