v3.26.1
Shareholder Report, Holdings (Details)
Feb. 28, 2026
C000015080 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 9.30% [1]
C000015080 [Member] | N A not applicable [Member]  
Holdings [Line Items]  
Percent of Total Investments 9.20% [1]
C000015080 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.70% [1]
C000015080 [Member] | Standard & Poor's, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.30% [1]
C000015080 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.10% [1]
C000015080 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 72.40% [1]
C000015080 [Member] | Investments Purchased with Collateral from Securities Lending [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.20%
C000015080 [Member] | Variable Rate Senior Loan Interests [Member]  
Holdings [Line Items]  
Percent of Total Investments 12.70%
C000015080 [Member] | Collateralized Mortgage-Backed Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.40%
C000015080 [Member] | Asset-Backed Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 10.60%
C000015080 [Member] | Preferred Stock [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.80%
C000015080 [Member] | Common Stock [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00%
C000015080 [Member] | Sovereign Debt [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.30%
C000015080 [Member] | Exchange Traded Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.30%
C000015080 [Member] | Repurchase Agreements [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.70%
C000015080 [Member] | Corporate Bond Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 55.00% [2]
C000015078 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 9.30% [3]
C000015078 [Member] | N A not applicable [Member]  
Holdings [Line Items]  
Percent of Total Investments 9.20% [3]
C000015078 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.70% [3]
C000015078 [Member] | Standard & Poor's, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.30% [3]
C000015078 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.10% [3]
C000015078 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 72.40% [3]
C000015078 [Member] | Investments Purchased with Collateral from Securities Lending [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.20%
C000015078 [Member] | Variable Rate Senior Loan Interests [Member]  
Holdings [Line Items]  
Percent of Total Investments 12.70%
C000015078 [Member] | Collateralized Mortgage-Backed Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.40%
C000015078 [Member] | Asset-Backed Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 10.60%
C000015078 [Member] | Preferred Stock [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.80%
C000015078 [Member] | Common Stock [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00%
C000015078 [Member] | Sovereign Debt [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.30%
C000015078 [Member] | Exchange Traded Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.30%
C000015078 [Member] | Repurchase Agreements [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.70%
C000015078 [Member] | Corporate Bond Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 55.00% [4]
C000015076 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 9.30% [5]
C000015076 [Member] | N A not applicable [Member]  
Holdings [Line Items]  
Percent of Total Investments 9.20% [5]
C000015076 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.70% [5]
C000015076 [Member] | Standard & Poor's, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.30% [5]
C000015076 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.10% [5]
C000015076 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 72.40% [5]
C000015076 [Member] | Investments Purchased with Collateral from Securities Lending [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.20%
C000015076 [Member] | Variable Rate Senior Loan Interests [Member]  
Holdings [Line Items]  
Percent of Total Investments 12.70%
C000015076 [Member] | Collateralized Mortgage-Backed Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.40%
C000015076 [Member] | Asset-Backed Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 10.60%
C000015076 [Member] | Preferred Stock [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.80%
C000015076 [Member] | Common Stock [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00%
C000015076 [Member] | Sovereign Debt [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.30%
C000015076 [Member] | Exchange Traded Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.30%
C000015076 [Member] | Repurchase Agreements [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.70%
C000015076 [Member] | Corporate Bond Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 55.00% [6]
C000015185 [Member] | Other [Member]  
Holdings [Line Items]  
Percent of Total Investments 12.60%
C000015185 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 10.90% [7]
C000015185 [Member] | N A not applicable [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.70% [7]
C000015185 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 27.00% [7]
C000015185 [Member] | Standard & Poor's, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.30% [7]
C000015185 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 12.80% [7]
C000015185 [Member] | Standard & Poor's, AAA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.70% [7]
C000015185 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 28.60% [7]
C000015185 [Member] | BRAZIL  
Holdings [Line Items]  
Percent of Total Investments 1.70%
C000015185 [Member] | CANADA  
Holdings [Line Items]  
Percent of Total Investments 2.10%
C000015185 [Member] | CHILE  
Holdings [Line Items]  
Percent of Total Investments 1.30%
C000015185 [Member] | ISRAEL  
Holdings [Line Items]  
Percent of Total Investments 0.80%
C000015185 [Member] | MEXICO  
Holdings [Line Items]  
Percent of Total Investments 3.10%
C000015185 [Member] | SAUDI ARABIA  
Holdings [Line Items]  
Percent of Total Investments 1.30%
C000015185 [Member] | SOUTH AFRICA  
Holdings [Line Items]  
Percent of Total Investments 0.80%
C000015185 [Member] | UNITED KINGDOM  
Holdings [Line Items]  
Percent of Total Investments 0.80%
C000015185 [Member] | UNITED STATES  
Holdings [Line Items]  
Percent of Total Investments 74.40%
C000015185 [Member] | TÜRKIYE  
Holdings [Line Items]  
Percent of Total Investments 1.10%
C000015185 [Member] | Investments Purchased with Collateral from Securities Lending [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.50%
C000015185 [Member] | Variable Rate Senior Loan Interests [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.70%
C000015185 [Member] | Collateralized Mortgage-Backed Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 27.50%
C000015185 [Member] | Asset-Backed Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 10.50%
C000015185 [Member] | Sovereign Debt [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.60%
C000015185 [Member] | Repurchase Agreements [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.20%
C000015185 [Member] | Corporate Bond Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 31.60% [8]
C000015185 [Member] | US Government Corporations and Agencies Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.40%
C000015187 [Member] | Other [Member]  
Holdings [Line Items]  
Percent of Total Investments 12.60%
C000015187 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 10.90% [9]
C000015187 [Member] | N A not applicable [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.70% [9]
C000015187 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 27.00% [9]
C000015187 [Member] | Standard & Poor's, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.30% [9]
C000015187 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 12.80% [9]
C000015187 [Member] | Standard & Poor's, AAA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.70% [9]
C000015187 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 28.60% [9]
C000015187 [Member] | BRAZIL  
Holdings [Line Items]  
Percent of Total Investments 1.70%
C000015187 [Member] | CANADA  
Holdings [Line Items]  
Percent of Total Investments 2.10%
C000015187 [Member] | CHILE  
Holdings [Line Items]  
Percent of Total Investments 1.30%
C000015187 [Member] | ISRAEL  
Holdings [Line Items]  
Percent of Total Investments 0.80%
C000015187 [Member] | MEXICO  
Holdings [Line Items]  
Percent of Total Investments 3.10%
C000015187 [Member] | SAUDI ARABIA  
Holdings [Line Items]  
Percent of Total Investments 1.30%
C000015187 [Member] | SOUTH AFRICA  
Holdings [Line Items]  
Percent of Total Investments 0.80%
C000015187 [Member] | UNITED KINGDOM  
Holdings [Line Items]  
Percent of Total Investments 0.80%
C000015187 [Member] | UNITED STATES  
Holdings [Line Items]  
Percent of Total Investments 74.40%
C000015187 [Member] | TÜRKIYE  
Holdings [Line Items]  
Percent of Total Investments 1.10%
C000015187 [Member] | Investments Purchased with Collateral from Securities Lending [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.50%
C000015187 [Member] | Variable Rate Senior Loan Interests [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.70%
C000015187 [Member] | Collateralized Mortgage-Backed Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 27.50%
C000015187 [Member] | Asset-Backed Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 10.50%
C000015187 [Member] | Sovereign Debt [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.60%
C000015187 [Member] | Repurchase Agreements [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.20%
C000015187 [Member] | Corporate Bond Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 31.60% [10]
C000015187 [Member] | US Government Corporations and Agencies Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.40%
C000151934 [Member] | Other [Member]  
Holdings [Line Items]  
Percent of Total Investments 12.60%
C000151934 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 10.90% [11]
C000151934 [Member] | N A not applicable [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.70% [11]
C000151934 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 27.00% [11]
C000151934 [Member] | Standard & Poor's, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.30% [11]
C000151934 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 12.80% [11]
C000151934 [Member] | Standard & Poor's, AAA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.70% [11]
C000151934 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 28.60% [11]
C000151934 [Member] | BRAZIL  
Holdings [Line Items]  
Percent of Total Investments 1.70%
C000151934 [Member] | CANADA  
Holdings [Line Items]  
Percent of Total Investments 2.10%
C000151934 [Member] | CHILE  
Holdings [Line Items]  
Percent of Total Investments 1.30%
C000151934 [Member] | ISRAEL  
Holdings [Line Items]  
Percent of Total Investments 0.80%
C000151934 [Member] | MEXICO  
Holdings [Line Items]  
Percent of Total Investments 3.10%
C000151934 [Member] | SAUDI ARABIA  
Holdings [Line Items]  
Percent of Total Investments 1.30%
C000151934 [Member] | SOUTH AFRICA  
Holdings [Line Items]  
Percent of Total Investments 0.80%
C000151934 [Member] | UNITED KINGDOM  
Holdings [Line Items]  
Percent of Total Investments 0.80%
C000151934 [Member] | UNITED STATES  
Holdings [Line Items]  
Percent of Total Investments 74.40%
C000151934 [Member] | TÜRKIYE  
Holdings [Line Items]  
Percent of Total Investments 1.10%
C000151934 [Member] | Investments Purchased with Collateral from Securities Lending [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.50%
C000151934 [Member] | Variable Rate Senior Loan Interests [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.70%
C000151934 [Member] | Collateralized Mortgage-Backed Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 27.50%
C000151934 [Member] | Asset-Backed Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 10.50%
C000151934 [Member] | Sovereign Debt [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.60%
C000151934 [Member] | Repurchase Agreements [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.20%
C000151934 [Member] | Corporate Bond Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 31.60% [12]
C000151934 [Member] | US Government Corporations and Agencies Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.40%
C000015189 [Member] | Other [Member]  
Holdings [Line Items]  
Percent of Total Investments 12.60%
C000015189 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 10.90% [13]
C000015189 [Member] | N A not applicable [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.70% [13]
C000015189 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 27.00% [13]
C000015189 [Member] | Standard & Poor's, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.30% [13]
C000015189 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 12.80% [13]
C000015189 [Member] | Standard & Poor's, AAA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.70% [13]
C000015189 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 28.60% [13]
C000015189 [Member] | BRAZIL  
Holdings [Line Items]  
Percent of Total Investments 1.70%
C000015189 [Member] | CANADA  
Holdings [Line Items]  
Percent of Total Investments 2.10%
C000015189 [Member] | CHILE  
Holdings [Line Items]  
Percent of Total Investments 1.30%
C000015189 [Member] | ISRAEL  
Holdings [Line Items]  
Percent of Total Investments 0.80%
C000015189 [Member] | MEXICO  
Holdings [Line Items]  
Percent of Total Investments 3.10%
C000015189 [Member] | SAUDI ARABIA  
Holdings [Line Items]  
Percent of Total Investments 1.30%
C000015189 [Member] | SOUTH AFRICA  
Holdings [Line Items]  
Percent of Total Investments 0.80%
C000015189 [Member] | UNITED KINGDOM  
Holdings [Line Items]  
Percent of Total Investments 0.80%
C000015189 [Member] | UNITED STATES  
Holdings [Line Items]  
Percent of Total Investments 74.40%
C000015189 [Member] | TÜRKIYE  
Holdings [Line Items]  
Percent of Total Investments 1.10%
C000015189 [Member] | Investments Purchased with Collateral from Securities Lending [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.50%
C000015189 [Member] | Variable Rate Senior Loan Interests [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.70%
C000015189 [Member] | Collateralized Mortgage-Backed Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 27.50%
C000015189 [Member] | Asset-Backed Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 10.50%
C000015189 [Member] | Sovereign Debt [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.60%
C000015189 [Member] | Repurchase Agreements [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.20%
C000015189 [Member] | Corporate Bond Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 31.60% [14]
C000015189 [Member] | US Government Corporations and Agencies Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.40%
[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 7.8% 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 7.8% 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 7.8% 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 12.0% 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 12.0% 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 12.0% 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 12.0% of $1,000 Par Preferred and/or Contingent Capital Securities.