BB or Lower [Member] N A not applicable [Member] N R not rated [Member] Short Term Treasury Debt [Member] Investments Purchased with Collateral from Securities Lending [Member] Structured Assets [Member] Government Bonds [Member] Short Term Government Agency Debt [Member] Investment companies [Member] Bloomberg U S Aggregate Bond Index [Member] Bloomberg U S Aggregate Bond C000202747 Index [Member] C000202747 [Member] Class W C000033991 [Member] Retirement Class C000014635 [Member] Class R6 C000079556 [Member] Premier Class C000162549 [Member] Class I C000033992 [Member] Class A Preferred Stock [Member] Common Stock [Member] Repurchase Agreements [Member] Bank Loan Obligations [Member] Corporate Bond Securities [Member] Standard & Poor's, BBB Rating [Member] Standard & Poor's, A Rating [Member] Standard & Poor's, AA Rating [Member] Moody's, Aaa Rating [Member] C000033995 [Member] C000162551 [Member] C000079558 [Member] C000014638 [Member] C000033994 [Member] Short Term Variable Rate Securities [Member] Bloomberg U S 1 3 Year Government Credit Bond Index [Member] C000202755 [Member] C000033275 [Member] C000033276 [Member] C000079571 [Member] C000162566 [Member] C000033274 [Member] C000033277 [Member] C000162567 [Member] C000079572 [Member] C000033279 [Member] C000033278 [Member] C000202756 [Member] ICE BofA BB B U S Cash Pay High Yield Constrained Index [Member] Bloomberg U S Aggregate Bond C000033284 Index [Member] Bloomberg U S Aggregate Bond C000202758 Index [Member] C000202758 [Member] C000033284 [Member] C000033285 [Member] C000079574 [Member] C000162569 [Member] C000033283 [Member] C000033286 [Member] C000162570 [Member] C000033287 [Member] Bloomberg Municipal Bond Index [Member] Bloomberg 10 Year Municipal Bond Index [Member] Rights Warrants [Member] C000202762 [Member] C000079523 [Member] C000079524 [Member] C000079525 [Member] C000162579 [Member] C000079526 [Member] C000117723 [Member] C000162598 [Member] C000117722 [Member] C000117721 [Member] C000117724 [Member] C000202767 [Member] C000158753 [Member] C000158750 [Member] C000158751 [Member] C000162603 [Member] C000158752 [Member] CANADA ECUADOR GERMANY IRELAND MEXICO UNITED ARAB EMIRATES UNITED KINGDOM UNITED STATES TÜRKIYE Turkey C000205813 [Member] C000205815 [Member] C000205812 [Member] C000205811 [Member] C000205814 [Member] Bloomberg MSCI U S Green Bond Index [Member] Supranational [Member] Other [Member] C000205819 [Member] C000205816 [Member] C000205817 [Member] C000205820 [Member] C000205818 [Member] SWEDEN NETHERLANDS KOREA, REPUBLIC OF JAPAN FRANCE Investment Type [Axis] Net Assets Investment Company Portfolio Turnover No Trading Symbol Flag