| **Subsequent Event**             | 6 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
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| **Subsequent Events [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
| Subsequent Event                 | Subsequent EventOn July 2, 2012, the Company completed the previously announced acquisition of Hardy Underwriting Bermuda Limited (Hardy), a specialized Lloyd's of London (Lloyd's) underwriter.  For the year ended December 31, 2011, Hardy reported gross written premiums of $430 million.  The closing of the acquisition followed approval of the transaction agreement by Hardy shareholders and regulatory approvals in various jurisdictions.  The purchase price for Hardy was approximately $230 million.  Acquisition related expenses incurred during the six months ended June 30, 2012, including investment advisory, legal and other expenses, were recorded in the Corporate and Other Non-Core Segment and were approximately $4 million.  Pursuant to requirements, the Company deposited approximately $230 million of British pound denominated short-term investments in escrow to fund the acquisition at the time the agreement was executed.  Foreign exchange losses on these escrow funds are included in Corporate and Other Non-Core Net realized investment gains (losses).The Company has not yet finalized the purchase accounting related to the acquisition of Hardy.  The Company estimates that the fair value of Hardy's assets will include approximately $55 million of identifiable indefinite-lived intangible assets and $80 million of identifiable finite-lived intangible assets, as well as the recognition of approximately $35 million of goodwill.  The goodwill is not expected to be deductible for tax purposes. |

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| - Definition
The entire disclosure for significant events or transactions that occurred after the balance sheet date through the date the financial statements were issued or the date the financial statements were available to be issued. Examples include: the sale of a capital stock issue, purchase of a business, settlement of litigation, catastrophic loss, significant foreign exchange rate changes, loans to insiders or affiliates, and transactions not in the ordinary course of business.
+ References
No definition available.
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