Australia's big four banks had their credit ratings cut by Standard & Poor's as a result of major changes in the criteria it uses to assess risk. ANZ, Commonwealth Bank, National Australia Bank and Westpac were each cut one notch to AA-minus, the fourth-highest credit rating on S&P's scale. Macquarie Group was cut by two levels to BBB, the ninth-highest grade. The ratings cuts though, have largely been ignored by investors in early trading, with all four of the big banks. Macquarie Group bucked the trend to be slightly lower on a day when the overall market was up about 0.2 per cent. ANZ shares were recently up 5 cents, or 0.2 per cent, to $20.55 while CBA added 20 cents, or 0.4 per cent, to $48.40. NAB gained 11 cents, or 0.4 per cent, to $24.28 and Westpac was up 5 cents, or 0.3 per cent to $21.18. Macquarie Group shares were down 9 cents, or 0.3 per cent, to $24.26. Little impact expected