Other [Member] N A not applicable [Member] N R not rated [Member] BB or Lower [Member] Investments Purchased with Collateral from Securities Lending [Member] C000042237 [Member] Class I C000171408 [Member] Class R6 C000042236 [Member] Class C C000042234 [Member] Class A Preferred Stock [Member] US Government Corporations and Agencies Securities [Member] Exchange Traded Funds [Member] Repurchase Agreements [Member] Corporate Bond Securities [Member] Standard & Poor's, BBB Rating [Member] Standard & Poor's, AA Rating [Member] UNITED STATES UNITED KINGDOM SWITZERLAND SPAIN NETHERLANDS MEXICO FRANCE FINLAND CANADA BERMUDA Standard & Poor's, A Rating [Member] Common Stock [Member] C000081597 [Member] C000081598 [Member] C000171409 [Member] C000081600 [Member] Structured Notes [Member] Convertible Preferred Securities [Member] Convertible Bonds [Member] Investment Type [Axis] Net Assets Investment Company Portfolio Turnover No Trading Symbol Flag