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Invesments (Aggregated Summarized Financial Information for Partnerhips in our Alternative Investment Portfolio) (Details) (USD $) | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2011 | Mar. 31, 2011 | Jun. 30, 2010 | Mar. 31, 2010 | Jun. 30, 2011 | Mar. 31, 2011 | Jun. 30, 2010 | Mar. 31, 2010
Net investment income |  | $ 132,600,000 |  | $ 125,600,000 |  | $ 286,800,000 |  | $ 274,400,000
Realized gains (losses) |  | 355,300,000 |  | (396,900,000) |  | 163,000,000 |  | (486,700,000)
Net change in unrealized appreciation |  | 608,300,000 |  | 810,300,000 |  | 2,072,500,000 |  | 1,248,800,000
Net income |  | 1,096,200,000 |  | 539,000,000 |  | 2,522,300,000 |  | 1,036,500,000
Net investment income earned | 39,345,000 |  | 36,545,000 |  | 82,818,000 |  | 71,251,000 |
Alternative Investments [Member] |  |  |  |  |  |  |  |
Net investment income earned | $ 7,900,000 |  | $ 4,900,000 |  | $ 19,500,000 |  | $ 8,800,000 |

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- Definition This item represents the disclosure of summarized financial information for unconsolidated subsidiaries and 50 percent-or-less owned entities accounted for using the equity method of accounting. If investments in common stock of corporate joint ventures or other investments accounted for under the equity method are, in the aggregate, material in relation to the financial position or results of operations of an investor, it may be necessary to present summarized information as to assets of the investee, or group of investments for which combined disclosure is appropriate, either by individual financial statement caption or in groups, as appropriate. Such summarized financial information may, at a minimum, include net income or loss. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph w -Article 1 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 08 -Paragraph g -Subparagraph 1, 2 -Article 4 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 159 -Paragraph 18 -Subparagraph f Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 18 -Paragraph 20 -Subparagraph d Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph bb -Article 1 + Details
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