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Investments (Aggregated Balance Sheet Summarized Financial Information for Partnerhips in our Alternative Investment Portfolio) (Details) (Details) (USD $) In Millions, unless otherwise specified | Sep. 30, 2012 | Sep. 30, 2011
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Investments [Abstract] |  |
Investments | $ 12,214 | $ 13,553
Total assets | 12,912 | 14,253
Total liabilities | 657 | 1,105
Partners' Capital | $ 12,255 | $ 13,148

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