v3.26.1
Shareholder Report, Holdings (Details)
Feb. 28, 2026
C000042237 [Member] | Other [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.60%
C000042237 [Member] | N A not applicable [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.80% [1]
C000042237 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.50% [1]
C000042237 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 69.70% [1]
C000042237 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.60% [1]
C000042237 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 21.40% [1]
C000042237 [Member] | UNITED STATES  
Holdings [Line Items]  
Percent of Total Investments 50.90%
C000042237 [Member] | UNITED KINGDOM  
Holdings [Line Items]  
Percent of Total Investments 12.20%
C000042237 [Member] | SWITZERLAND  
Holdings [Line Items]  
Percent of Total Investments 4.90%
C000042237 [Member] | SPAIN  
Holdings [Line Items]  
Percent of Total Investments 5.10%
C000042237 [Member] | NETHERLANDS  
Holdings [Line Items]  
Percent of Total Investments 1.30%
C000042237 [Member] | MEXICO  
Holdings [Line Items]  
Percent of Total Investments 1.00%
C000042237 [Member] | FRANCE  
Holdings [Line Items]  
Percent of Total Investments 9.30%
C000042237 [Member] | FINLAND  
Holdings [Line Items]  
Percent of Total Investments 1.10%
C000042237 [Member] | CANADA  
Holdings [Line Items]  
Percent of Total Investments 11.70%
C000042237 [Member] | BERMUDA  
Holdings [Line Items]  
Percent of Total Investments 0.90%
C000042237 [Member] | Investments Purchased with Collateral from Securities Lending [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.10%
C000042237 [Member] | Preferred Stock [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.20%
C000042237 [Member] | US Government Corporations and Agencies Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.70%
C000042237 [Member] | Exchange Traded Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.20%
C000042237 [Member] | Repurchase Agreements [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.50%
C000042237 [Member] | Corporate Bond Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 85.30% [2]
C000171408 [Member] | Other [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.60%
C000171408 [Member] | N A not applicable [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.80% [3]
C000171408 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.50% [3]
C000171408 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 69.70% [3]
C000171408 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.60% [3]
C000171408 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 21.40% [3]
C000171408 [Member] | UNITED STATES  
Holdings [Line Items]  
Percent of Total Investments 50.90%
C000171408 [Member] | UNITED KINGDOM  
Holdings [Line Items]  
Percent of Total Investments 12.20%
C000171408 [Member] | SWITZERLAND  
Holdings [Line Items]  
Percent of Total Investments 4.90%
C000171408 [Member] | SPAIN  
Holdings [Line Items]  
Percent of Total Investments 5.10%
C000171408 [Member] | NETHERLANDS  
Holdings [Line Items]  
Percent of Total Investments 1.30%
C000171408 [Member] | MEXICO  
Holdings [Line Items]  
Percent of Total Investments 1.00%
C000171408 [Member] | FRANCE  
Holdings [Line Items]  
Percent of Total Investments 9.30%
C000171408 [Member] | FINLAND  
Holdings [Line Items]  
Percent of Total Investments 1.10%
C000171408 [Member] | CANADA  
Holdings [Line Items]  
Percent of Total Investments 11.70%
C000171408 [Member] | BERMUDA  
Holdings [Line Items]  
Percent of Total Investments 0.90%
C000171408 [Member] | Investments Purchased with Collateral from Securities Lending [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.10%
C000171408 [Member] | Preferred Stock [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.20%
C000171408 [Member] | US Government Corporations and Agencies Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.70%
C000171408 [Member] | Exchange Traded Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.20%
C000171408 [Member] | Repurchase Agreements [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.50%
C000171408 [Member] | Corporate Bond Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 85.30% [4]
C000042236 [Member] | Other [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.60%
C000042236 [Member] | N A not applicable [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.80% [5]
C000042236 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.50% [5]
C000042236 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 69.70% [5]
C000042236 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.60% [5]
C000042236 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 21.40% [5]
C000042236 [Member] | UNITED STATES  
Holdings [Line Items]  
Percent of Total Investments 50.90%
C000042236 [Member] | UNITED KINGDOM  
Holdings [Line Items]  
Percent of Total Investments 12.20%
C000042236 [Member] | SWITZERLAND  
Holdings [Line Items]  
Percent of Total Investments 4.90%
C000042236 [Member] | SPAIN  
Holdings [Line Items]  
Percent of Total Investments 5.10%
C000042236 [Member] | NETHERLANDS  
Holdings [Line Items]  
Percent of Total Investments 1.30%
C000042236 [Member] | MEXICO  
Holdings [Line Items]  
Percent of Total Investments 1.00%
C000042236 [Member] | FRANCE  
Holdings [Line Items]  
Percent of Total Investments 9.30%
C000042236 [Member] | FINLAND  
Holdings [Line Items]  
Percent of Total Investments 1.10%
C000042236 [Member] | CANADA  
Holdings [Line Items]  
Percent of Total Investments 11.70%
C000042236 [Member] | BERMUDA  
Holdings [Line Items]  
Percent of Total Investments 0.90%
C000042236 [Member] | Investments Purchased with Collateral from Securities Lending [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.10%
C000042236 [Member] | Preferred Stock [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.20%
C000042236 [Member] | US Government Corporations and Agencies Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.70%
C000042236 [Member] | Exchange Traded Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.20%
C000042236 [Member] | Repurchase Agreements [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.50%
C000042236 [Member] | Corporate Bond Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 85.30% [6]
C000042234 [Member] | Other [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.60%
C000042234 [Member] | N A not applicable [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.80% [7]
C000042234 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.50% [7]
C000042234 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 69.70% [7]
C000042234 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.60% [7]
C000042234 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 21.40% [7]
C000042234 [Member] | UNITED STATES  
Holdings [Line Items]  
Percent of Total Investments 50.90%
C000042234 [Member] | UNITED KINGDOM  
Holdings [Line Items]  
Percent of Total Investments 12.20%
C000042234 [Member] | SWITZERLAND  
Holdings [Line Items]  
Percent of Total Investments 4.90%
C000042234 [Member] | SPAIN  
Holdings [Line Items]  
Percent of Total Investments 5.10%
C000042234 [Member] | NETHERLANDS  
Holdings [Line Items]  
Percent of Total Investments 1.30%
C000042234 [Member] | MEXICO  
Holdings [Line Items]  
Percent of Total Investments 1.00%
C000042234 [Member] | FRANCE  
Holdings [Line Items]  
Percent of Total Investments 9.30%
C000042234 [Member] | FINLAND  
Holdings [Line Items]  
Percent of Total Investments 1.10%
C000042234 [Member] | CANADA  
Holdings [Line Items]  
Percent of Total Investments 11.70%
C000042234 [Member] | BERMUDA  
Holdings [Line Items]  
Percent of Total Investments 0.90%
C000042234 [Member] | Investments Purchased with Collateral from Securities Lending [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.10%
C000042234 [Member] | Preferred Stock [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.20%
C000042234 [Member] | US Government Corporations and Agencies Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.70%
C000042234 [Member] | Exchange Traded Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.20%
C000042234 [Member] | Repurchase Agreements [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.50%
C000042234 [Member] | Corporate Bond Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 85.30% [8]
C000081597 [Member] | N A not applicable [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.00% [9]
C000081597 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 6.20% [9]
C000081597 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 42.50% [9]
C000081597 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.00% [9]
C000081597 [Member] | Standard & Poor's, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.50% [9]
C000081597 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 34.80% [9]
C000081597 [Member] | Investments Purchased with Collateral from Securities Lending [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.40%
C000081597 [Member] | Preferred Stock [Member]  
Holdings [Line Items]  
Percent of Total Investments 6.50%
C000081597 [Member] | Repurchase Agreements [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.20%
C000081597 [Member] | Corporate Bond Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 72.00% [10]
C000081597 [Member] | Common Stock [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.40%
C000081597 [Member] | Structured Notes [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.40%
C000081597 [Member] | Convertible Preferred Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.60%
C000081597 [Member] | Convertible Bonds [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.50%
C000081598 [Member] | N A not applicable [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.00% [11]
C000081598 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 6.20% [11]
C000081598 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 42.50% [11]
C000081598 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.00% [11]
C000081598 [Member] | Standard & Poor's, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.50% [11]
C000081598 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 34.80% [11]
C000081598 [Member] | Investments Purchased with Collateral from Securities Lending [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.40%
C000081598 [Member] | Preferred Stock [Member]  
Holdings [Line Items]  
Percent of Total Investments 6.50%
C000081598 [Member] | Repurchase Agreements [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.20%
C000081598 [Member] | Corporate Bond Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 72.00% [12]
C000081598 [Member] | Common Stock [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.40%
C000081598 [Member] | Structured Notes [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.40%
C000081598 [Member] | Convertible Preferred Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.60%
C000081598 [Member] | Convertible Bonds [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.50%
C000171409 [Member] | N A not applicable [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.00% [13]
C000171409 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 6.20% [13]
C000171409 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 42.50% [13]
C000171409 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.00% [13]
C000171409 [Member] | Standard & Poor's, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.50% [13]
C000171409 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 34.80% [13]
C000171409 [Member] | Investments Purchased with Collateral from Securities Lending [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.40%
C000171409 [Member] | Preferred Stock [Member]  
Holdings [Line Items]  
Percent of Total Investments 6.50%
C000171409 [Member] | Repurchase Agreements [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.20%
C000171409 [Member] | Corporate Bond Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 72.00% [14]
C000171409 [Member] | Common Stock [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.40%
C000171409 [Member] | Structured Notes [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.40%
C000171409 [Member] | Convertible Preferred Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.60%
C000171409 [Member] | Convertible Bonds [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.50%
C000081600 [Member] | N A not applicable [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.00% [15]
C000081600 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 6.20% [15]
C000081600 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 42.50% [15]
C000081600 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.00% [15]
C000081600 [Member] | Standard & Poor's, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.50% [15]
C000081600 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 34.80% [15]
C000081600 [Member] | Investments Purchased with Collateral from Securities Lending [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.40%
C000081600 [Member] | Preferred Stock [Member]  
Holdings [Line Items]  
Percent of Total Investments 6.50%
C000081600 [Member] | Repurchase Agreements [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.20%
C000081600 [Member] | Corporate Bond Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 72.00% [16]
C000081600 [Member] | Common Stock [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.40%
C000081600 [Member] | Structured Notes [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.40%
C000081600 [Member] | Convertible Preferred Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.60%
C000081600 [Member] | Convertible Bonds [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.50%
[1] The ratings disclosed are the highest rating given by one of the following national rating agencies: Standard & Poor’s (S&P), Moody’s Investors Service, Inc. (Moody’s) or Fitch, Inc (Fitch). This treatment of split-rated securities may differ from that used for other purposes, such as for Fund investment policies. Credit ratings are subject to change. AAA, AA, A, and BBB are investment grade ratings; BB, B, CCC, CC, C and D are below-investment grade ratings. Holdings designated N/R are not rated by these national ratings agencies.
[2] Includes 84.0% of $1,000 Par Preferred and/or Contingent Capital Securities.
[3] The ratings disclosed are the highest rating given by one of the following national rating agencies: Standard & Poor’s (S&P), Moody’s Investors Service, Inc. (Moody’s) or Fitch, Inc (Fitch). This treatment of split-rated securities may differ from that used for other purposes, such as for Fund investment policies. Credit ratings are subject to change. AAA, AA, A, and BBB are investment grade ratings; BB, B, CCC, CC, C and D are below-investment grade ratings. Holdings designated N/R are not rated by these national ratings agencies.
[4] Includes 84.0% of $1,000 Par Preferred and/or Contingent Capital Securities.
[5] The ratings disclosed are the highest rating given by one of the following national rating agencies: Standard & Poor’s (S&P), Moody’s Investors Service, Inc. (Moody’s) or Fitch, Inc (Fitch). This treatment of split-rated securities may differ from that used for other purposes, such as for Fund investment policies. Credit ratings are subject to change. AAA, AA, A, and BBB are investment grade ratings; BB, B, CCC, CC, C and D are below-investment grade ratings. Holdings designated N/R are not rated by these national ratings agencies.
[6] Includes 84.0% of $1,000 Par Preferred and/or Contingent Capital Securities.
[7] The ratings disclosed are the highest rating given by one of the following national rating agencies: Standard & Poor’s (S&P), Moody’s Investors Service, Inc. (Moody’s) or Fitch, Inc (Fitch). This treatment of split-rated securities may differ from that used for other purposes, such as for Fund investment policies. Credit ratings are subject to change. AAA, AA, A, and BBB are investment grade ratings; BB, B, CCC, CC, C and D are below-investment grade ratings. Holdings designated N/R are not rated by these national ratings agencies.
[8] Includes 84.0% of $1,000 Par Preferred and/or Contingent Capital Securities.
[9] The ratings disclosed are the highest rating given by one of the following national rating agencies: Standard & Poor’s (S&P), Moody’s Investors Service, Inc. (Moody’s) or Fitch, Inc (Fitch). This treatment of split-rated securities may differ from that used for other purposes, such as for Fund investment policies. Credit ratings are subject to change. AAA, AA, A, and BBB are investment grade ratings; BB, B, CCC, CC, C and D are below-investment grade ratings. Holdings designated N/R are not rated by these national ratings agencies.
[10] Includes 35.8% of $1,000 Par Preferred and/or Contingent Capital Securities.
[11] The ratings disclosed are the highest rating given by one of the following national rating agencies: Standard & Poor’s (S&P), Moody’s Investors Service, Inc. (Moody’s) or Fitch, Inc (Fitch). This treatment of split-rated securities may differ from that used for other purposes, such as for Fund investment policies. Credit ratings are subject to change. AAA, AA, A, and BBB are investment grade ratings; BB, B, CCC, CC, C and D are below-investment grade ratings. Holdings designated N/R are not rated by these national ratings agencies.
[12] Includes 35.8% of $1,000 Par Preferred and/or Contingent Capital Securities.
[13] The ratings disclosed are the highest rating given by one of the following national rating agencies: Standard & Poor’s (S&P), Moody’s Investors Service, Inc. (Moody’s) or Fitch, Inc (Fitch). This treatment of split-rated securities may differ from that used for other purposes, such as for Fund investment policies. Credit ratings are subject to change. AAA, AA, A, and BBB are investment grade ratings; BB, B, CCC, CC, C and D are below-investment grade ratings. Holdings designated N/R are not rated by these national ratings agencies.
[14] Includes 35.8% of $1,000 Par Preferred and/or Contingent Capital Securities.
[15] The ratings disclosed are the highest rating given by one of the following national rating agencies: Standard & Poor’s (S&P), Moody’s Investors Service, Inc. (Moody’s) or Fitch, Inc (Fitch). This treatment of split-rated securities may differ from that used for other purposes, such as for Fund investment policies. Credit ratings are subject to change. AAA, AA, A, and BBB are investment grade ratings; BB, B, CCC, CC, C and D are below-investment grade ratings. Holdings designated N/R are not rated by these national ratings agencies.
[16] Includes 35.8% of $1,000 Par Preferred and/or Contingent Capital Securities.