Asbestos and environmental reinsurance retention.

No definition available.

Name:	cinf_AsbestosAndEnvironmentalReinsuranceRetention
Namespace Prefix:	cinf_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Increase in the recovery of liability for unpaid claims and claims adjustment expense, incurred claims, prior years.

+ References

No definition available.

+ Details

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Namespace Prefix:	cinf_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Carrying amount as of the balance sheet date of reserves for the costs of settling insured claims and costs incurred in the claims settlement process attributable to environmental claims related to mold.

+ References

No definition available.

+ Details

Name:	cinf_LiabilityForAsbestosAndEnvironmentalClaimsMold
Namespace Prefix:	cinf_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Percentage of reserves for asbestos and environmental claims to total loss and loss expense reserves.

+ References

No definition available.

+ Details

Name:	cinf_PercentageOfReservesForAsbestosAndEnvironmentalClaims
Namespace Prefix:	cinf_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Carrying amount as of the balance sheet date of reserves for the costs of settling insured claims and costs incurred in the claims settlement process attributable to asbestos and environmental claims, net of estimated reinsurance recoveries.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 40

-Section 50

-Paragraph 3

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6482485&loc=d3e14764-158437

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount needed to reflect the estimated ultimate cost of settling claims relating to insured events that have occurred on or before the balance sheet date, whether or not reported to the insurer at that date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 40

-Section 50

-Paragraph 3

-Subparagraph (a),(b),(c)

-URI http://asc.fasb.org/extlink&oid=6482485&loc=d3e14764-158437

+ Details

Name:	us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of expense for claims incurred in prior reporting periods and related claims settlement costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 235

-Section S99

-Paragraph 3

-Subparagraph (SX 210.12-18)

-URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e575016-122915

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 18

-Article 12

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

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- Details

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- Details

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- Details

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Property Casualty Loss And Loss Expenses (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Certain accident, life and health loss reserves	$ 4,438,000,000	$ 4,241,000,000	$ 4,169,000,000	$ 4,280,000,000
Prior year claims and claims adjustment expense	(98,000,000)	(147,000,000)	(396,000,000)
Increase in favorable reserve developement on prior accident	49,000,000	249,000,000
Net loss and loss expense reserves for asbestos and environmental claims	81,000,000	77,000,000
Environmental claims related to mold	51,000,000	51,000,000
Percentage of reserves for asbestos and environmental claims	2.00%	1.90%
Maximum
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Reinsurance retention	500,000
Certain Accident, Life and Health Lines
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Certain accident, life and health loss reserves	47,000,000	70,000,000	61,000,000
Commercial Insurance
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Prior year claims and claims adjustment expense	(57,000,000)	(95,000,000)	(292,000,000)
Commercial Insurance \| Workers' Compensation Line
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Prior year claims and claims adjustment expense	(51,000,000)	(14,000,000)	(74,000,000)
Commercial Insurance \| Commercial Property Line
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Prior year claims and claims adjustment expense	(34,000,000)	(22,000,000)
Commercial Insurance \| Homeowner Line
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Prior year claims and claims adjustment expense	(14,000,000)	(19,000,000)	(52,000,000)
Commercial Insurance \| Commercial Casualty Line
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Prior year claims and claims adjustment expense	5,000,000	(70,000,000)	(177,000,000)
Commercial Insurance \| Commercial Auto Line
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Prior year claims and claims adjustment expense	39,000,000
Personal Insurance
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Prior year claims and claims adjustment expense	(12,000,000)	(39,000,000)	(99,000,000)
Excess and Surplus Lines Insurance
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Prior year claims and claims adjustment expense	$ (29,000,000)	$ (13,000,000)	$ (5,000,000)