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Summary Of Significant Accounting Policies (Narrative) (Details)	12 Months Ended
	Dec. 31, 2018 USD ($) state subsidiary independent_insurance_agency reporting_locations	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2008
Significant Accounting Policies
Unrealized gains reclassified to retained earnings for ASU 2016-01, after tax	$ 2,503,000,000
Income Tax Examination, Penalties Expense	$ 0
Number of operating subsidaries \| subsidiary	2
Number of independent insurance agencies \| independent_insurance_agency	1,757
Number of reporting locations \| reporting_locations	2,344
Number of states in which entity operates \| state	42
Defined Benefit Plan Qualifying Age				40 years
Current fair value of the BOLI invested assets and cash exceeded the current fair value of the contract holders' account value	$ 3,000,000	$ 29,000,000
Other invested assets	123,000,000	103,000,000
Depreciation expense	31,000,000	28,000,000	$ 30,000,000
Land, building and equipment impairments	0	0	0
Total	$ 402,000,000	(148,000,000)	(124,000,000)
Minimum
Significant Accounting Policies
Estimated useful lives	3 years
Maximum
Significant Accounting Policies
Estimated useful lives	39 years 6 months
Life Policy Loans
Significant Accounting Policies
Other invested assets	$ 33,000,000	31,000,000
Venture Capital Funds
Significant Accounting Policies
Other invested assets	60,000,000	35,000,000
Real Estate Investment
Significant Accounting Policies
Other invested assets	$ 30,000,000	$ 37,000,000
10 Largest States
Significant Accounting Policies
Generated percentage of total earned premiums	58.40%	59.70%
Ohio, Largest State
Significant Accounting Policies
Generated percentage of total earned premiums	15.90%	16.20%
Illinois, Georgia, Indiana, North Carolina and Pennsylvania \| Minimum
Significant Accounting Policies
Generated percentage of total earned premiums	5.00%
Illinois, Georgia, Indiana, North Carolina and Pennsylvania \| Maximum
Significant Accounting Policies
Generated percentage of total earned premiums	6.00%
Largest Single Agency Relationship
Significant Accounting Policies
Generated percentage of total earned premiums	0.80%
All Other \| Maximum
Significant Accounting Policies
Generated percentage of total earned premiums	4.00%
Stock Options
Significant Accounting Policies
Weighted-average remaining contractual life for options expected to vest	10 years
Property Casualty Insurance Segment
Significant Accounting Policies
Number of operating subsidaries \| subsidiary	2
Stock Options
Significant Accounting Policies
Awards vesting period	3 years
Restricted Stock Units (RSUs)
Significant Accounting Policies
Awards vesting period	3 years
Equity Securities
Significant Accounting Policies
Total	$ 395,000,000	$ (120,000,000)	(99,000,000)
Unrealized Gain (Loss) on Investments	$ 404,000,000	$ 0	$ 0