Net Assets Investment Company, Portfolio Turnover C000253819 [Member] American Funds® U.S. Small and Mid Cap Equity Fund - Class A C000253818 [Member] American Funds® U.S. Small and Mid Cap Equity Fund - Class C C000253817 [Member] American Funds® U.S. Small and Mid Cap Equity Fund - Class F-1 C000253816 [Member] American Funds® U.S. Small and Mid Cap Equity Fund - Class F-2 C000253815 [Member] American Funds® U.S. Small and Mid Cap Equity Fund - Class F-3 C000253807 [Member] American Funds® U.S. Small and Mid Cap Equity Fund - Class 529-A C000253825 [Member] American Funds® U.S. Small and Mid Cap Equity Fund - Class 529-C C000253824 [Member] American Funds® U.S. Small and Mid Cap Equity Fund - Class 529-E C000253822 [Member] American Funds® U.S. Small and Mid Cap Equity Fund - Class 529-F-2 C000253821 [Member] American Funds® U.S. Small and Mid Cap Equity Fund - Class 529-F-3 C000253814 [Member] American Funds® U.S. Small and Mid Cap Equity Fund - Class R-1 C000253813 [Member] American Funds® U.S. Small and Mid Cap Equity Fund - Class R-2 C000253812 [Member] American Funds® U.S. Small and Mid Cap Equity Fund - Class R-2E C000253811 [Member] American Funds® U.S. Small and Mid Cap Equity Fund - Class R-3 C000253810 [Member] American Funds® U.S. Small and Mid Cap Equity Fund - Class R-4 C000253808 [Member] American Funds® U.S. Small and Mid Cap Equity Fund - Class R-5E C000253809 [Member] American Funds® U.S. Small and Mid Cap Equity Fund - Class R-5 C000253826 [Member] American Funds® U.S. Small and Mid Cap Equity Fund - Class R-6 Russell Midcap Index [Member] Russell 2500 Index [Member] Russell 3000 Index [Member] Investment Type [Axis] Financial Services Sector [Member] Healthcare Sector [Member] Short Term Securities And Other Assets Less Liabilities [Member] Short-term securities & other assets less liabilities [Member]