Other Assets and Liabilities Net [Member] Taxable Municipal Bonds [Member] C000105308 [Member] Institutional Plus Shares C000024520 [Member] Institutional Shares C000007058 [Member] Admiral Shares C000046841 [Member] ETF Shares C000007057 [Member] Investor Shares Sovereign Debt [Member] US Government Corporations and Agencies Securities [Member] Corporate Bond Securities [Member] C000046842 [Member] C000209800 [Member] C000024522 [Member] C000105309 [Member] C000105311 [Member] C000105310 [Member] C000007061 [Member] C000046843 [Member] C000007060 [Member] C000007062 [Member] C000046844 [Member] C000007063 [Member] C000007064 [Member] C000081425 [Member] C000170279 [Member] Institutional Select Shares Asset Backed Commercial Mortgage Backed Securities [Member] Over 25 Years [Member] Twenty To 25 Years [Member] Fifteen To 20 Years [Member] Ten To 15 Years [Member] Five To 10 Years [Member] Zero To 5 Years [Member] C000054351 [Member] C000054350 [Member] C000054349 [Member] C000075027 [Member] C000075028 [Member] Investment Type [Axis] Net Assets Investment Company Portfolio Turnover No Trading Symbol Flag