Commonwealth Bank risks losing bragging rights as the Big Four bank with the highest retail customer satisfaction rating - a position it has held since the end of 2012.According to the latest Roy Morgan Research consumer banking customer satisfaction survey, CBA's rating has fallen over the past six months while its peers have all gained ground.In August, 81 per cent of CBA customers said they were satisfied with the bank. Close behind were Westpac and National Australia Bank - each scoring 80.7 per cent. ANZ's satisfaction rating was 79.7 per cent.CBA's rating fell 1.1 percentage points over the six months to August, while NAB's rating rose 40 basis points over the same period, ANZ's rose 1.8 percentage points and Westpac's rose 2.7 percentage points.CBA has taken a hit over its financial planning scandal.One feature of the Big Bank ratings is how close they are. In the past the gap between first and fourth could be as much as ten percentage points. Now it is 1.3 percentage points.Overall, Victoria Teachers Mutual Bank leads the survey with a rating of 97.9 per cent, followed by Teachers Mutual Bank (89.9 per cent) and ING Direct (89.7 per cent).Roy Morgan's industry communications director, Norman Morris, said the average rating of 82.3 per cent was an 18-year high.