All four major Australian banks had their credit rating on long term debt lowered to Aa2 from Aa1 by Moody's Investors Service, with the outlook revised from negative to stable.Moody's placed the banks on review for a downgrade in February. The downgrade brings the credit rating for the big banks into line with the AA- ratings for banks from Standard & Poor's.The ratings for the banks' subordinated debt were also downgraded, to Aa3 from Aa2, Moody's said.The lower ratings also apply to Bank of Western Australia, a subsidiary of Commonwealth Bank.Ratings remain under review for the subsidiaries of each bank in New Zealand.In the announcement, and explaining the rationale for the ratings change, Moody's noted that the long term ratings of major banks "continue to incorporate two notches of uplift from systemic support", or the expectation, well-supported by responses to the financial crisis, that the major banks in Australia can expect plenty of active assistance from the government and the central bank.On a stand-alone basis, the long-term debt rating of major banks would be A1, and for subordinated debt the rating would be A2.