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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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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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Other investments not otherwise specified in the taxonomy.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Summary Of Significant Accounting Policies (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 entity state	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2008
Significant Accounting Policies [Line Items]
Number of operating subsidaries	2
Number of independent insurance agencies	1,408
Number of reporting locations	1,758
Number of states in which entity operates	39
Defined Benefit Plan Qualifying Age				40 years
Contingent commission accrual	$ 102	$ 68
Percentage points contributed to the property casualty	3.10%
Depreciation expense	37	46	40
Land, building and equipment impairments	0	0	0
Weighted-average remaining contractual life for exercisable awards	3 years 2 months 12 days
Current fair value of the BOLI invested assets and cash exceeded the current fair value of the contract holders' account value	77
Other invested assets	68	66
Minimum [Member]
Significant Accounting Policies [Line Items]
Estimated useful lives	3 years
Maximum [Member]
Significant Accounting Policies [Line Items]
Estimated useful lives	39 years 6 months
Life Policy Loans [Member]
Significant Accounting Policies [Line Items]
Other invested assets	37
Venture Capital Funds [Member]
Significant Accounting Policies [Line Items]
Other invested assets	$ 31
10 Largest States [Member]
Significant Accounting Policies [Line Items]
Generated percentage of total earned premiums	65.40%	66.50%
Ohio, Largest State [Member]
Significant Accounting Policies [Line Items]
Generated percentage of total earned premiums	19.10%	19.50%
Georgia, Illinois, Indiana, Michigan, North Carolina, Pennsylvania and Virginia [Member] \| Minimum [Member]
Significant Accounting Policies [Line Items]
Generated percentage of total earned premiums	4.00%
Georgia, Illinois, Indiana, Michigan, North Carolina, Pennsylvania and Virginia [Member] \| Maximum [Member]
Significant Accounting Policies [Line Items]
Generated percentage of total earned premiums	8.00%
Largest Single Agency Relationship [Member]
Significant Accounting Policies [Line Items]
Generated percentage of total earned premiums	0.90%
All Other [Member] \| Maximum [Member]
Significant Accounting Policies [Line Items]
Generated percentage of total earned premiums	2.10%
Restricted Stock Units [Member]
Significant Accounting Policies [Line Items]
Awards vesting period	3 years
Stock Options [Member]
Significant Accounting Policies [Line Items]
Awards vesting period	3 years
Weighted-average remaining contractual life for exercisable awards	10 years