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Summary Of Significant Accounting Policies (Narrative) (Details)		12 Months Ended
	Feb. 28, 2019	Dec. 31, 2020 USD ($) independent_insurance_agency subsidiary state reporting_locations	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2008
Significant Accounting Policies
Income Tax Examination, Penalties Expense		$ 0
Number of operating subsidaries \| subsidiary		2
Number of independent insurance agencies \| independent_insurance_agency		1,848
Number of reporting locations \| reporting_locations		2,578
Number of states in which entity operates \| state		45
Excess (deficit) of Separate Account Fair Value over (under) Contract Holder Account Value		$ 99,000,000	$ 52,000,000
Minimum participant age to elect					40 years
Other invested assets		348,000,000	296,000,000
Depreciation expense		33,000,000	25,000,000	$ 31,000,000
Land, building and equipment impairments		0	0	$ 0
Increase to allowance through retained earnings for ASU 2016-13, after-tax			2,000,000
Covid-19 pandemic-related incurred loss and expenses		85,000,000
Premium Receivable, Allowance for Credit Loss		19,000,000
Premium Receivable, Allowance for Credit Loss, Property Casualty Premiums Receivable		$ 9,000,000
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	32,000,000
Venture Capital Funds
Significant Accounting Policies
Other invested assets		128,000,000	71,000,000
Real Estate Investment
Significant Accounting Policies
Other invested assets		25,000,000	29,000,000
Other than Securities Investment
Significant Accounting Policies
Other invested assets		$ 162,000,000	$ 164,000,000
10 Largest States
Significant Accounting Policies
Generated percentage of total earned premiums		53.30%	54.80%
Ohio, Largest State
Significant Accounting Policies
Generated percentage of total earned premiums		14.80%	15.10%
Illinois, Georgia, North Carolina, Indiana and Pennsylvania \| Minimum
Significant Accounting Policies
Generated percentage of total earned premiums		4.00%
Illinois, Georgia, North Carolina, Indiana 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		1.30%
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
Cincinnati Global
Significant Accounting Policies
Goodwill		$ 30,000,000	$ 30,000,000
Syndicate capacity - indefinite lived		$ 31,000,000	$ 31,000,000
Broker Relationships and Internally developed technology \| Cincinnati Global \| Minimum
Significant Accounting Policies
Useful life	5 years
Broker Relationships and Internally developed technology \| Cincinnati Global \| Maximum
Significant Accounting Policies
Useful life	15 years