Independent Insurance Agencies and Brokerages

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Number of Locations

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Number of Subsidiaries

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Percentage of earned premiums.

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Contingent commission accrual as percentage points to the property casualty combined ratio.

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The charge against earnings resulting from the aggregate write down of all assets from their carrying value to their fair value.

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Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date.

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The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation.

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The carrying amount as of the balance sheet date of the combined total of loss contingency liabilities.

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Amount of the cumulative effect of the change in accounting principle or new accounting pronouncement on retained earnings or other components of equity or net assets in the statement of financial position as of the beginning of the earliest period presented.

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Amount of the effect of a change in accounting principle on basic earnings per share.

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The number of states the entity operates in as of the balance sheet date.

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Other investments not otherwise specified in the taxonomy.

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The maximum useful life of long-lived, physical assets used in the normal conduct of business and not intended for resale. Examples include land, buildings, machinery and equipment, and other types of furniture and equipment including, but not limited to, office equipment, furniture and fixtures, and computer equipment and software.

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The minimum useful life of long lived, physical assets used in the normal conduct of business and not intended for resale. Examples include land, buildings, machinery and equipment, and other types of furniture and equipment including, but not limited to, office equipment, furniture and fixtures, and computer equipment and software.

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Fair value amount of the specified investment category of assets maintained in separate accounts as of the balance sheet date.

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Summary of Significant Accounting Policies - Additional Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 Year Location Entity State	Dec. 31, 2010	Dec. 31, 2009
Significant Accounting Policies [Line Items]
Number of operating subsidaries	2
Number of independent insurance agencies	1,312
Number of reporting locations	1,648
Number of States in which Entity Operates	39
Contingent commission accrual	$ 68	$ 77	$ 81
Percentage points contributed to the property casualty	2.20%
Estimated useful lives	3
Estimated useful lives	39.5
Depreciation expense	46	40	48
Land, building and equipment impairments	0	0	0
Capital lease obligation	17
Current fair value of the BOLI invested assets and cash exceeded the current fair value of the contract holders' account value	42
Other invested assets	66	84
Life Policy Loans
Significant Accounting Policies [Line Items]
Other invested assets	37
Venture Capital Funds
Significant Accounting Policies [Line Items]
Other invested assets	29
Accounting Standards Update 2010-26
Significant Accounting Policies [Line Items]
Cumulative effect of change in accounting for other-than-temporary impairments as of April 1, 2009, net of tax	20
Reduction in shareholder's equity book value per share	$ 0.12
Retained Earnings
Significant Accounting Policies [Line Items]
Cumulative effect of change in accounting for other-than-temporary impairments as of April 1, 2009, net of tax			106
Accumulated Other Comprehensive Income (Loss)
Significant Accounting Policies [Line Items]
Cumulative effect of change in accounting for other-than-temporary impairments as of April 1, 2009, net of tax			$ (106)
10 largest states
Significant Accounting Policies [Line Items]
Generated percentage of total earned premiums	66.50%	67.10%
Ohio, largest state
Significant Accounting Policies [Line Items]
Generated percentage of total earned premiums	19.50%	20.50%
Georgia, Illinois, Indiana, Michigan, North Carolina, Pennsylvania and Virginia \| Minimum
Significant Accounting Policies [Line Items]
Generated percentage of total earned premiums	4.00%
Georgia, Illinois, Indiana, Michigan, North Carolina, Pennsylvania and Virginia \| Maximum
Significant Accounting Policies [Line Items]
Generated percentage of total earned premiums	8.00%
Largest single agency relationship
Significant Accounting Policies [Line Items]
Generated percentage of total earned premiums	1.20%
All Other \| Maximum
Significant Accounting Policies [Line Items]
Generated percentage of total earned premiums	2.10%