The era of Aa and AA graded Australian bank credit ratings is almost over. Could it be B, C or D ratings for any bank of note before long?The profit reporting schedule this week is ANZ, NAB, Macquarie and Westpac next Monday. A CBA update, who knows when, but the bank must parry the final report of the APRA prudential inquiry, so maybe CBA will report early in this week's profit season. S&P downgraded six entities to A+ from AA-, including CBA's Colonial Mutual Life Assurance Society, ANZ's OnePath Life and Westpac's life insurance arm. Colonial Holding Co and ANZ Wealth Australia were downgraded to A from A+ two years ago.It's single A ratings for the industry before long for each of ANZ, Westpac, CBA and NAB, little but cynicism in banking credit quality encouraged by Ken Hayne's royal commission. At present these banks are rated AA- by S&P and Aa3 by Moody's.In June 2017 Moody's Investors Service downgraded the Baseline Credit Assessments, long-term ratings and Counterparty Risk Assessments of 12 Australian banks and their affiliates."Bank failures are very often associated with systemic crises driven by macroeconomics rather than idiosyncratic factors," Moody's said at the time. "[Our] country level analysis focuses on economic strength, institutional strength, susceptibility to event risk, credit conditions, funding conditions and industry structure."Idiosyncratic, endogenous and even fatal for some banks, the present crisis of legitimacy twinned with a crisis of confidence flourishes amid a fair dinkum credit crunch in Australia.Margins, payout ratios, cash profits and total shareholder return will be no more than footnotes to this year's profit season. Vulnerable dividends and profits laden with provision will be the talking points of the next week.