Schedule Of Industry Concentrations Held In Corporate Portfolio Based On Fair Value (Detail)	Dec. 31, 2012
Commitments and Contingencies Disclosure [Line Items]
Insurance	18.00%
Electric utilities and services	17.00%
Banks	8.00%
Oil and gas extraction	6.00%
Pipelines	6.00%
Transportation	5.00%
Mining	4.00%
Chemicals	3.00%
Telecommunications	3.00%
REITs	3.00%

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Proportion Of Banking Industry Concentration At Fair Value In Corporate Portfolio

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Proportion Of Chemicals Industry Concentration At Fair Value In Corporate Portfolio

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Proportion Of Electric Industry Concentration At Fair Value In Corporate Portfolio

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Proportion Of Insurance Industry Concentration At Fair Value In Corporate Portfolio

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Proportion Of Mining Industry Concentration At Fair Value In Corporate Portfolio

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Proportion Of Oil And Gas Industry Concentration At Fair Value In Corporate Portfolio

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Proportion Of Pipelines Industry Concentration At Fair Value In Corporate Portfolio

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Proportion Of REIT Industry Concentration At Fair Value In Corporate Portfolio

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Proportion Of Telecommunications Industry Concentration At Fair Value In Corporate Portfolio

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Proportion Of Transportation Industry Concentration At Fair Value In Corporate Portfolio

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