Net Assets Investment Company, Portfolio Turnover C000025132 [Member] U.S. Government Securities Fund® - Class A C000025139 [Member] U.S. Government Securities Fund® - Class C C000025140 [Member] U.S. Government Securities Fund® - Class F-1 C000068600 [Member] U.S. Government Securities Fund® - Class F-2 C000025136 [Member] U.S. Government Securities Fund® - Class R-4 C000164800 [Member] U.S. Government Securities Fund® - Class R-5E C000025137 [Member] U.S. Government Securities Fund® - Class R-5 C000077855 [Member] U.S. Government Securities Fund® - Class R-6 C000179952 [Member] U.S. Government Securities Fund® - Class F-3 C000025141 [Member] U.S. Government Securities Fund® - Class 529-A C000025143 [Member] U.S. Government Securities Fund® - Class 529-C C000025144 [Member] U.S. Government Securities Fund® - Class 529-E C000224557 [Member] U.S. Government Securities Fund® - Class 529-F-2 C000224558 [Member] U.S. Government Securities Fund® - Class 529-F-3 C000025133 [Member] U.S. Government Securities Fund® - Class R-1 C000025134 [Member] U.S. Government Securities Fund® - Class R-2 C000148357 [Member] U.S. Government Securities Fund® - Class R-2E C000025135 [Member] U.S. Government Securities Fund® - Class R-3 Bloomberg U.S. Government/Mortgage Backed Securities Index [Member] Bloomberg U.S. Aggregate Index [Member] Investment Type [Axis] U S Treasury Bonds And Notes [Member] U.S. Treasury bonds & notes [Member] Mortgage-backed obligations [Member] Federal Agency Bonds And Notes [Member] Federal agency bonds & notes [Member] Options purchased [Member] Short Term Securities And Other Assets Less Liabilities [Member] Short-term securities & other assets less liabilities [Member]